You can add IK's to your skeleton and bake them out alongside the rest. The trick is finding the proper plane for the IK pole vectors. Most people find this by finding the triangle formed by the shoulder, elbow and wrist (or hip, knee and ankle), then finding the midpoint of the line from the first to the last piece, getting the middle of that line, and pushing the pole from that point out along the line towards the mid point
You may find cases where the elbow or knee locks; if that happens just skip that key and rely on the ones before or after.
There are lots of tricks to improve the results but this is the core of the algorithm.