Yes .. click Add to Library, then Select Sub-Set in the window that pops open. Take the X out of Universe, then X every part you want to save the pose for. Probably a good idea to put 'pp' or something in the pose name, so you know it's a partial pose.

I should add that I've found it best to save poses with IK turned OFF. With it on you risk getting odd results when the partial pose is applied, and it also doubles the size of the pose file, unnecessarily.