i don't have any experience with d3d vertex buffers but from my understanding it only could be done flawlessly if it were possible to write your own mesh loader (best for a format which supports two uv-sets so that you don't have to do hacks like using two different versions of a mdl7 file).

just replacing the uvs like in jcl's example isn't enough. you could load a light map uv-set but it still had to use uv-patches with the seams at the same place in the topology as the other uv-map (don't know how to explain it better). this isn't very useful...

i could be wrong though.

it also would be nice if models could react to the brightness below them just like with bsp light maps but probably this currently wouldn't easily work either.