I think Multi texturing in the light mapper is still W.I.P
Whether it will be fixed in the steam version I don't know..... it should be just a case of leaving the Texture field blank in the fpe
If that works and looks ok then you have done it right.
If however you use the light mapper and it all goes wrong then I would say its still down to that ..
The only person ever to get all his work done by "Friday" was Robinson crusoe