I've had an experiment with Milkshape/Bodyshop/SimPE and created an everyday clothing mesh for males with a pregnancy morph. I used one of the Maxis meshes as a base and with much help from the meshing tutorials on MTS2 got it to work by simply cloning the fat mesh group then modifying it to look pregnant and amending the text in the comment accordingly. The texture is just something I did quickly in Photoshop, but if people are interested then I will do some tweaking/proper recolours and upload it (probably to MTS2, unless there is a better suggestion). Piccies of the mesh in action below:
(I might cave in and buy H&M but I'm not sure it's worth it for a couple of meshes.)