You can add a keep alive to nearly any decoder if you know what you're doing.
Basically, it requires hooking the positive keep alive wire to the function common supply (the blue wire, or whatever powers the LEDs for the headlight and backup light) and soldering the negative keep alive wire to the decoder negative supply. Often, this can be accomplished by soldering the wire to the negative side of one of the 4 rectifier diodes found on many decoders.
If either of you can post a photo of the decoder (close-up, hi-rez), we may be able to figure out where to attach the keep alive wires.
Here's a web page that tells you how to do this in general, with specific examples (unfortunately, not the decoder in the MRC/MP units).
http://www.members.optusnet.com.au/mainnorth/alive.htmJohn C.