This isn't my original idea, but one that I got from one of the weaving lists.  Still, it's a good one, I think.  I rarely warp front to back, but when I do I grab this little teddy bear and use it as my cross holder.  I tie him to the breast beam and then use his arms and legs to hold the cross.  It would be better if I had one with the arms and legs sticking straight up, but this one does fine.  And he's cute.