I've bent tips on a wood stove.  Done it several different ways.  1.  Just heat the belly good and hot until it bends by hand or in a form.  I have used oil and done it without as I temper.   2.  I read on a post some time back, (believe it might have been Toomanyknots) to soak a towel, wrap the limb with it, cover with foil and heat.  Tried it and it worked really well.  No real trick to either.  Thicker wood might require a strap on the belly to keep it from splintering.