...small update, I've tried DX3DRipper and NinjaRipper, DX3D was terrible, all my geometry was distorted & half was missing. Ninja was a bit better but also had missing geometry and only lightmaps with no textures.
However both programs did extract lightmaps so I guess it's at least possible. If I could get lightmap UV's they could be manually applied in MED and then all is left is importing lightmap-texture files extracted with DX3D or Ninja.