Creating new animation clip from blend of two others

Is this possible inside Unity? The use case is we can't use mecanim due to performance reasons. And the solutions that work best for our use case don't support layer blending. But our use case would be ok with just creating pre blended animations. It's for npc's where I'm fine with waiting for a clip to complete before transitioning into the next animation. So for our half dozen core combat animations we just create walk/run/standing variations of each.

Or is there a third party tool that would work better? Say exporting fixing it there then importing them back in?

 

have you tried lerp (slerp) at 0.5?

or do you want to record transitions as animations? then maybe scene motion capture

but I guess you mean upperbody animations. to record you can use smc.
but to edit the length you will need an animation editor asset or skele's dae exporter.