One advanced PT suggested a Styrofoam cylinder to lay on for the same purpose of releasing and dropping the shoulders and such.

I found I like the large inflatable exercise balls even better - i use a 26" one.

I lay face up on it to do the TOS type pec/shoulder releases
also great for laying over on belly to stretch the hips and spine
also lean on it sideways while sitting on the floor with arm over it to stretch the pecs and roll on it to stimulate the lymph flow in that area too

just sitting on it and rocking uses core and leg muscles and side to side uses obliques/core/legs