If you are as handy with a soldering iron as you are with a Dremel, then installing a third pot is a cinch. All you need to do is find a wiring diagram from a Jazz bass and copy that - 2 vols and one tone to the output jack. Or if you want something a bit extra, using your two existing pot holes as a spacing template, route two more in, add a 4th for a toggle, and give it Les Paul wiring. Which is what happened to many EB3s ultimately. OR..keep the two holes, change the vol to a jazz bass/Danelectro stacked pot and have two vols in one space. Brosnac's Guitar Electronics is the bible, and has all these wiring tips and diagrams (like cartoon illustrations for dummies like me ) out the yang. You can find it on ebay, Amazon, order it at bookstores, and chances are you can get it like I did through the public library.
So many options...
I also suggest checking out the hot mini-humbucker pups from DiMarzio and Duncan as they will look EB3 correct, but have a bit more ooomph, and will blend in with the not-so-muddybucker a bit more usefully.