I know it's not possible on one figure in one animation (P7) so I used 2 jessies - one with IK on feet and hands the other only on feet - hope the result is good. First "swap" takes place in 18 second, second one in 42.
No bvh used.

Be warned: she's naked.

http://www.youtube.com/watch?v=McLCBFB5o4M

Outstanding :)

Your method?
Enquiring minds need to know.

Basicly there are keyframes (KF) every 10th frame - I didn't have any particular picture of what the final result should look like so I kept all the KF as they came up (it helped a lot).

2 "walk cycles" are used - first when she's crawling and second one while walking up the stairs (for that I made a python script that mirrors all necesarry parameters and offsets them in directions I need - so it takes "no time" to see the result of some "walk cycles").

Overlaping of Jessies takes about 2 seconds - I mean same poses are applied to both of them for 2 seconds before "swap".

I found that working with IK on hands was not easy (that was the first time I used it and it was quite difficult).

I made already 15 seconds longer animation where at the begginig she wakes up, turns around and starts crawling but it still needs some tweaking - and it's not easy while IK is on - so maybe I'll add 3rd Jessie with no IK at all). 

Great job!

 As I've already said on YouTube: This is pretty dang awesome! I love it when she's swinging in her arms - that's something I've never seen in a Poser animation before. Great job!

Thanks for good comments.
Actually that part when she's jumping was quite easy and I finished that very fast - only  "timing" didn't go so smooth (you can see she is moving faster when falling down) and that's because there is a  "change of figure" while she is in the air - when she grabs the bar there is already IK on hands.

Incredible piece of animation!  The integration is flawless.  Great job!