There is one thing you can do.

Ask the vendors to add an outfitter converted version of their clothing to their product for their customers convenience. It just takes a few minutes to create one.

If they do this, they will certainly try the outfit on V4WM and in case there are problems, they will either correct it in the weightmaps or leave it out completely. If they add it, it will be an additional incentive for potential buyers to get the product. 

If you can get a few popular vendors on this track, it will surely catch on with the others.

Most of the clothing will need very little or no adjustment at all - and (some) of their customers will do it themselves anyway, so it should of benefit the to vendors as well