The hot iron method that you tried is good, but it depends on how bad the crushing is, as sometimes it is bad enough to sever fibres.
If you still have enough sapwood/heartwood and the bow is at the start of tillering work down sapwood an extra 1/16". If not, burnish the whole back.
Otherwise you could burnish the back, then sand the surface, then back with rawhide. I would back a yew bow if it is going to be used for hunting, not for any worries about it breaking in tension with a pristine back, but as protection against getting dings in it.
Hamish.