Hey BonBun,
One thing I've tried is to modify the avatar.blend skeleton to a larger size. You can lengthen or shorten the bones as you need. It's important to leave the skeleton in the T-Pose though. The dae files don't record rotations. Instead of trying to use a mesh body (I'm assuming you are using either sculpts and/or prims for the bodies) , I make a very small ball and attach it to the skeleton, same as you would a mesh body at the hip and assign the weights there. That hides the mesh part. This is exported as a dae (both ball and skeleton together) and uploaded to SL. You may need to adjust your hip offset though. Best to try on the Beta grid to save $L.
Once you're uploaded, wear the mesh. It will distort your avatar. Then you can add attachments/body parts. Once you get the hip offset like you need, you can use regular animations with the modyfied body, even dance animations.
I'm not quarenteeing how good this will work, I'm still learning the possibilities with mesh and what you can do. But it's worth a try.
One other option would be to use viewer 1.23 and upload your deforms. I'm not sure but some of the 3rd party viewers might can be used to upload deforms as well. The cool thing about deforms is that you can make the ones you need, upload, and change out different offsets quickly without having to make a whole mesh/skeleton. Then again, being able to use normal animations with the mesh/skeleton is very cool too.
If you like, get in touch with me in-world and I'll show you one of my tests for a giant werewolf.
Burtrum