Simply blocking in the arms using just a few key frames on the contacts and passing positions. It's already passable as an arm swing, but it needs a lot of tweaking and refining to really get the flexibility in there. Once I've blocked in the rest of the keys and got them looking smooth I'll probably look at trying to overlap sections and get some nice shoulder rotation in there.
I'm not entirely sure how I'm going to go about posing the arms for maximum overlapability (that is totally a word!) - Moom lacks individual controls for each limb segment, as I've mentioned before, so precisely controlling the position of his arms is going to be quite tricky. Not entirely sure how to find a way around that.
Looking at it again I also see that something weird has happened to his up and down positions; there's a very sudden jerk downwards after the second 'up' pose and I have no idea where that's come from. The key frames are identical so I can only assume Softimage is doing something weird with the interpolation?