Garnett, I also need a longer-than-average stock--my gunsmith says I have "ape-hanger arms." But I usually just put a Pachmayr or Limbsaver pullover pad on shotguns. Easy to apply, ugly-but-removable, and very effective in recoil reduction.
My hunting buddies tend to be purists and hate these "butt condoms" but they do admit that they help keep the gun from falling over when set against a tree, fence, or pickup, and they do avoid some scratching from brush and "bobwire," which a permanent pad won't do. I call 'em "butt body armor."
The one negative of this solution for me is that you have to remove the pad and dry off the stock wood after any dew or rain contact (not presently a big problem out here, unfortunately....). But that takes all of ten seconds.
Mike Armstrong