Linking two users on different volumes

Say I have Snow Leopard installed on volume A, and I have a user named kddi.

I also have Lion installed on volume B, and I also have a user named kddi.

However, when I look at the other kddi's homedir on the volume that I didn't start up on, I don't have access rights. Instead of assigning two users access rights to everything on each homedir, is there a way to tell each OS to recognize the two kddi's as the same Mac user?