apologies for the low res photo. just cleaning the inside of my phatty, look what fits right in there (if you removed the front part of the phatty underneath.
the metal blends in perfectly. and the sound?
immense.
nice looking phrankenphatty!
funny you are bringing this up today. For the first time last night i was toying around with my LP and my Line 6 uber metal.
i got some really good tones out of that combo too 
Here I was thinking you were soliciting ideas. 
The first thing that popped into my head was one of those nice clear rubber caster wheels. I like your idea better though.