This is a bit of an old topic, but it relates to two active bugs, 8357
(affecting Everquest) and 14608 (affecting Warhammer Online)
The rough summary of the situation is that these two games use d3dx9_30
and d3dx9_34 respectively, and at least the former uses
ConvertToIndexedBlendedMesh.
Anyway,
The only other option I'm aware of is to await the shader-based fixed
function pipeline replacement which might contain an implementation of
the D3DRS_VERTEXBLEND renderstates.
I worked on a pipeline replacement using GL_ARB_vertex_program a few months
ago but hit some roadblocks, so I never
