I've been meaning to try this in the next few days myself and hadn't gotten to it.  I have painted on a figure with multiple material zones (a shirt with three zones), but that is after importing with Kuroyume's plugin, which appears to use OBJ format behind the scenes but I haven't really dug into it that hard.  Hadn't actually tried importing the base object outside of his plugin but I suspect it can be made to work.  I suggest you ask Spanki or Kuroyume0161 via PM how you should go about this in general terms, both are pretty helpful (of course they might just reply here in the thread too).

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