So I really would like to use IPA instead of naptha/xylene as very high grade stuff is easily available for about $8/L. Would it be possible to carry out my standard stb but instead of seperation I can put it in a freezer at -40C for about 1-2 hours then just filter out the ice from IPA. Would dmt precipitate to the sides of the container?

Don't think that would be working. IPA is miscible with water so you would get only 1 phase. When you put your IPA/Water mixture into the freezer it will freeze as one liquid you won't get liquid IPA and frozen water. (Much like Wodka cannot freeze at 0°C)