Great Aircraft! Help With Crossfeed?

I'm having lots of fun with this aircraft.

I've been able to assign feathering to the stops on my twin Saitek proplevers, and they work

I've installed Ray's fabulous black cockpit texture (so it matches my homebuild cockpit).

I've added some nice switch sounds from the AVSIM library (Cockpitsounds).

And because the Aztec engine sounds, although nice, are a little bit lacking in bass, they don't work well with my Buttkicker vibration device, and so (sacrillege, probably) I've swapped over the bassier engine sounds from the Milviz Baron B55.

In all I'm powering around the Caribbean with this beauty and I just don't want to fly anything else.

One question, though, trying both native FSX control assignments and FSUIPC,I cannot get any button or keyboard switch to assign for the crossfeed controls. I'm really struggling with it, which is a shame, beecause I can cut an engine, feather a prrop and practice all kinds of single-engined manoeuvres, but without a crossfeed assignment I'm a bit stuck. (As I said I have a home cockpit build and don't like to use the VC if at all possible).

Any help appreciated!