Merging armatures with keyframes or merging NLA tracks

So I just finished making a spider walking animation. Unfortunately, I had the brilliant idea of making each leg a separate armature. This means that the animation involves 8 separate NLA tracks, which is a problem because I want at least a dozen of these guys running around at different speeds. Is there a way to join armatures while preserving keyframe data, or to merge multiple NLA tracks into a single action?