Well, you guys know me--I don't like to recommend anything without trying it, so I went ahead and installed a concentric pot for controlling both volume (lower knob) and tone (upper knob). See photo below. The concentric volume/tone control pot I used is a 500K/500K CTS pot I got from Warmoth. Excellent quality pot! They also sell the concentric knobs to fit it. The total for the three parts was $21. As I mentioned previously, unless you do quite a bit of clean playing through the bridge pickup, the Cabronita does just fine without a tone control. But you guys know me--I like to have control, so I thought I'd go ahead and try out this modification. Works like a charm. For the wiring, I used a diagram I came across on the TDPRI forums, which also incorporates a treble bleed to keep the output from getting muddy when the volume is turned down. Turned out that it had the connections from the toggle switch common lug and the output jack "hot" lead switched on the volume pot, so the tone control didn't work initially, but swapping those two wires fixed that. Corrected wiring diagram attached below.

The photo of the concentric pot knobs also shows the replacement bridge I installed--it's a American Strat hardtail bridge, Fender P/N 003-2909-000. I don't understand why this isn't original equipment on the Thinline Cabronita, as it aligns much better with the Fidelitron pickup pole pieces and gives a more comfortable spacing between the E strings and the edges of the fretboard. One note of caution, though--the width between the two outside mounting holes is about 1/8" narrower than the stock bridge, so when installing it on the body, you need to mount the middle screw first and then angle the two outside screws to fit the holes in the body. Torque the two outside screws down evenly/carefully and you'll have no problem. The string-through hole spacing of the bridge vs. the body is also correspondingly narrower, but there's still enough overlap on the outside holes to get the strings through without a problem.