Why not use the old "cow" model cold ones with a squig as the head? Remove the front legs, little bit of putty, and now you are cooking with gas as they say. Should look quite nice, and although the conversion may be pricy, I suspect you could get the bitz to do it fairly easily in a trade or on Ebay.
What ever your freind does, try and let us know, plenty of people would be interested in non-boar ork cavalry.