When I had to fix this problem for my Heline character (based on Posette) before 3DCommune would agree to sell it, what I did was use the Grouping tool to set the nostrils aside as a separate material. Since Mike already has nostrils as a material, you can use the Grouping tool to add polygons to the nostril material until you're satisfied. I'd go that route and skip the whole UVMapper thing altogether.