in case it helps anyone, here's a quick workaround - I think there's a better way without using multiple versions of a character, but this works and may help someone somewhere for the moment

in this example, you've got Figure1 as your character and the BVH is 100 frames

1. Load Figure1 and import the BVH file
2. Save the pose at frame 100 to the library
3. Load another copy of Figure1 (I'll call it Figure2 here), turn off all IK and apply the pose you just saved
4. Select the Hip of Figure2 and use the X,Z Transforms to get the figure into the center of the Body object (the red circle that appears when you select the Body)
5. Make sure you're on frame 100, select the Body of Figure2 and move it until it's positioned exactly over Figure1
6. Set the Body scaling on both figures so that at frame 0, Figure1=100%/Figure2=0% and at frame 100 Figure1=0%/Figure2=100%
7. Go to the animation pallette, drop down to Figure1->Body->Scale - select all keyframes from 0-100 and apply a Constant selection. Do the same for Figure2 so that both figures instantly change scale at frame 100
8. frame 100 should now have the character posed correctly and re-centred to the Body object - applying poses etc to Figure2 will now stay in place as the body parts are back in the center of the Body object