I have a Dead Mint Y2K excel that I got in a trade. It was a showroom piece until recently. It has the Single Fatboy pickup, and the Vol/Treble/Bass controls. I would like to upgrade to the Q-Filter, but from what I've seen that would be only 2 knobs, Vol/Filter. Is there another 3 knob configuration? If not should I just put a Dummy pot in there so the knobs look correct, and leave no empty holes?

Add a Q switch to the filter.  The rotating knob is the low pass filter.  Adding a Q means adding a flip switch, either two-way or three-way.  You'll have two knobs and one switch - three in total.  More flexibility in tone, easy and relatively cheap!  Who could ask for more?
 
Bill, tgo

Hey Guys,
 
I've always loved the Excel as is, with it's original design. If I were to ever consider modifying one, I'd add a tone control to roll off some of it's bite.  I think that would make a bigger improvement than adding a Q switch. It would have 4 controls rather than 3: Vol, Bass, Treble, & Tone.  
 
Rami