I can suggest giving your friend a tiny tiny dose. Part of my reason for being interested in psychedelic science, is because I think some folks need less rather than more.
I am similar, but never had enough DMT to be sure at what larger dose I might see. Although going by what else I had, I think no effect is likely with DMT in me. Unless a tiny tiny dose.
From a good 30-40-50g blue meanie mushrooms in youth, nothing, so seemingly.
From blue meanies in large dose recently, nothing, but while walking in the field they grow, is a blast of new knowledge from.
From Hicuri in a ceremony with Shaman, nothing, only my blood pressure dropped and I can't hold myself upright, but keep listening to the songs.
From Ayahuasca, again in a ceremony, almost the whole night I can't hold myself up, then one time I am called by a Shaman back into my body, and I begin seeing I am in the sky having a talk with the Virgin Mary, who is escorting me back into my body, because the Shaman is asking me to sit up. Which is not nothing.
Within two traditions I know, SantoDiame/UDV, and also indigenous australian, it is regarded as normal for certain persons to have no visionary experiences direct while the substance is being metabolized. I read that Santo Diame and UDV apply a special status to such persons.
Within indigenous australian tradition, Duboisia hopwoodii, can have two markedly distinct effects, and is known for this. It can cause anybody to feel incapable of staying upright, and lying down apparently unconscious for three days and nights, with three thousand lives of dreaming within the forms Mother Nature awards. Sinking into the soil below, becoming worms, grass, animals eating the grass, and so on and so forth, and everybody who had the experience is happy enough with. Or, it can cause anybody to feel capable of walking through a desert without water for three days and nights. It is planted at either end of every major desert walking route in outback australia. That is unless the cattle ate it all by now. But indigenous cowboys all know and use it still. With me, when I chewed Pituri (D.hopwoodii), it is just like I start thinking, "hell, no way am I going to just lie down in this, anything could happen, I have to stay awake", and then the only way to stay awake is to engage in physical exertion. The indigenous Ngungkari who gave me permission to use Pituri, knew that I won't be looking, and will be working.
So here is a bit of a big clue. There is not no psycho-active impact. And in fact, for folks who don't get the visionary aspect, what happens is that their/our behaviour and attitude and questioning and everything about set and setting, but most of all behaviour and surrounding sounds, will unfold out into nightly dreams over a number of years to come.
I know I am going to use a psychedelic, because I begin having dreams in the patterns of a new experience I didn't already live at the ground in my body. Normally I experience knew knowledge before dreaming of, but others are the other way around, however this difference is like half and half of the population have it each way, and is unrelated to the psychedelic experience. Yet if my body starts to go like the other half the population, learning in dreams before by experience, then I start to suspect a psychedelic, and begin observing my environment in dreams in case I find somebody wants me to have some, and then if I find anybody giving it to me in a dream, I go ahead and use. This is the traditional way to know it is safe. Sometimes if I am not feeling ready, but dreaming with a Ngungkari who thinks I should, it can be like being pestered into it in dreams.
I think also, it is significant, that there are a few times when I see visions, apart from in dreaming asleep at night. And each of those times, is close in time, with very very low doses of psychedelics. For example, the strongest vision I ever had came out of one joint of cannabis. Also I have had a vision from just Calea zakatechichi. Other men I know who are similar to myself, (in the indigenous community here are many more than among non-indigenous), suggest that why we don't see, is only because the dose is too large.
Remember it is not that there is actually no effect, but that the immediate effect is more a clairsentience (feelings based), rather than clairvoyance (vision based), and the visions will come along in time in dreams. I expect many traditional Curandero in Amazonia are similarly different, but no point telling those who don't want to believe. It can be very convenient, to get all one needs know, from just a whiff/sip of Ayahuasca, and then also be able drink as much as anybody else, but stay more sober. I remember also a talk by Dennis McKenna, where he said that at a science conference in Brazil, everybody got given a small cup of Ayahuasca, but only the gringos needed a second cup.
a mother a daughter a lover of life, an exorcist of addictions if ere in need of the strife, and at bottom line a wife, I might well be a bore, yet have no doubt, I stand among the poor, and beg not what for, that hat hath at, nobody's mind fell too flat