It's difficult because, while iPi Mocap Studio's mocap quality is very nice, it may not be quite accurate enough for props held by two hands, especially after applying motions to a character with different body proportions.
There are ways to work around the issue though. If the motion is going through a dedicated animation package, you can use IK and pinning to adjust the mocap data. This is how we made Toullie play a ukulele and Sergeant Marshmallow handle a harmonic with two paws in this video:
Excerpt from 'Brudders 2' (A Work In Progress)In our case, we're using Motion Builder but I think most 3D animation programs have some way to do this. Generally, we have nulls on the props that serve as constraints for the paws. When a paw come near it's target null, we gradually activate the constraint and the paw sticks to where it needs to be, and it stays there until we dial the effect down again.
Hope this helps.
G.