Source NAT Multiple Times on Same Device

Hi All,

I would like to source NAT traffic twice on my device. See the scenario below:

I have two Routing Instances, A and B. My default route for A is to table B. I want all traffic that will take the default route to be NAT'd to an address before it reaches routing instance B. I want routing instance B to only have a route for the source nat pool back to Routing Instance A rather than having to share all of my routes from RI A to routing instance B. 

Is this possible without configuring another Routing Instance that acts as a 'staging instance' or another physical interface interface that acts as the same?