In reply to pasbury:
You could do that listed above but no doubt you already pulling, pushing, twisting and grabbing as part of you bouldering work out.
Google the following three items below, watch the videos and perform 3 sets of 10 reps of each of these exercises as part of your warm up. Work up to be able to do 3 sets of 20, then add weight.
The range of movement is small, dont bend your arms, do it often, it wont impact your time on the wall climbing
Scapula pull up
Scapula push up
Scapula dip