getting rid of partial transparency and/or forcing PS not to use it?

I have a shop at Cafepress. For awhile now, they have been offering dark t-shirts that allow transparent PNG's to be used. Unfortunately, the printing process for dark shirts leaves white wherever partial transparency is present, which usually leaves a white halo around images and text.

Is there any way to force PS to not use partial transparency? Partial transparency looks great on white shirts, because the different printing process sees it as another form of white. It would be great to be able to toggle between usage and nonusage of partial transparency.

You can save for web in PNG-8 mode which dithers the partial transparency areas, but it also drops the color count down to a level that makes the design look bad. So far, that's the only way I can see to remove the partial transparency from already finished designs.

Any help would be appreciated.

not personally heard of anything like that, the easiest thing i can thing of is to make a black layer under your design and erase it (w/ a hard edge) so that it forms a very narrow black border around your design, merge and then use that. the transparency where you erased should work and although CP say blackon a design comes out different to the black T-shirt material your border should not be too noticeable.