I would not amend the planting holes at all (but dig them *big*, to provide a large area of well-broken-up soil for roots to readily spread out into). You want the roots to go elsewhere, not just stay curling round and round the planting hole b/c the soil is so much nicer there. If you just HAVE to chuck something into the planting hole, add some bone meal, but I do not think it really matters much. Again, get it spread out over the whole large wide area, not just right under the plant.
I also would not treat the roots with anything, unless a lot are very broken and the plant seems to have really insufficient root mass for survival in which case you can try LIGHTLY (!) dusting on a little woody-plant rooting hormone, which I can't prove helps but IME it *seems* to.
The biggest thing is to keep the plant watered without being soggy, and (for these decent-sized trees) stake it so it doesn't blow over before it has a real root system grown back. You may not get 100% survival but if it's a good deal on basically healthy trees it can still be worth the loss rate.
Good luck, have fun,
Pat