You could try a cheap pad like this: Fleece Western Wider Wither Pad - Statelinetack.com
It raises the front about 0.5", but that makes a difference. I use it to keep the saddle off of my horses' high withers, but it also seems to help with their shoulders. Both horses seem MUCH more comfortable when I use it than when I don't. And for $8, it doesn't break the bank.
Also, it tapers smoothly from pad to no pad. I tried a felt wool version, but it had a solid edge that caused problems.