I was doing something like that before as well, or rather I wrote an OBJ exporter/ save entity mesh as OBJ using the regular file_str_write instructions. If you don't need skins (which I didn't at first) this is quick and easy to do, as ent_create works with OBJ files as well!

I needed skins and some extra stuff, but unlike you I had the bitmap filenames, as my source was not a MDL file.

Apart from that, I totally forgot about obj.