Many years ago, Curious Labs came out with a program called Avatar Lab. These 2 animated swimming poses were included. Now, this is way before V4, but I applied them to V4 and to be honest, only some slight tweeking would be necessary. I know it doesn't really help, but I just thought I'd show them.

Now, I'm not sure, but I think there might be some swimming BVH files around somewhere, because I have a 139 frame animated swimming pose, and that's the only way I can think of that I got it.