Sync'd layer but different mask

I'm trying to setup a sync'd layer with a mask and it doesn't seem to apply the mask.
So, is it even possible to have a layer sync'd to another layer but with a mask?

my layers:

• Base movement layer (idle, walk, run, flying, etc...)
  
• An override layer (attacks, hits, etc...)
  
• An upper body layer (sync override layer, but with upper body mask)

This would allow me to say play an attack animation, while running or flying, or play a full attack animation with leg movement while idle on ground.

Right now any changes I make in the override layer have to be manually duplicated in the upper body layer. If I could sync the layers but add a mask, it would save me a ton of extra work. Feature request?

Thanks.