I'm not sure what you're asking. If you have a dual-homed setup, then referring to devices by their Private address will tell the machine to use the private network. If you use their "public" name, then the public side will be used.
If you're hell-bent on using DNS in this case - you would need dual DNS entries (one for the private, one of the public).
----------------------------------------------------------------------------------
Your lack of planning does not constitute an emergency on my part...unless you're my manager...or a director and above...or a really loud-spoken end-user..All right - what was my emergency again?