Hey there, Alex.
There are a couple of ways to go about it. If you have a lot of spares, you could forage around for body parts (sorry for being a little graphic) that would more or less approximate the pose you want. Of course, it presupposes that the parts should be from the same subject (US Infantry figure parts for US Infantry subjects).
A more radical technique would be to saw the parts at the joints, drill holes into the center, and insert copper wire onto each cut-up piece. The part could then be reattached and, with the copper wire, could be repositioned to your desire. The joint could then be filled with putty and sanded conformably.
Hope this helps.