On the (always excellent) advice of paults I ordered a Behringer FS112B 2-button footswitch. It was new in box, never used, $28 with shipping (they often go for $15 used). I was attracted to it as opposed to other similar options because it uses a single TRS cable, I wanted to leave the other switch jack open for an expression pedal in case I don't get a floor controller soon. And no batteries/PS like some other options)
I plugged it in, assigned Switch Ring to Rig Up, and Switch Tip to Rig Down, and that's it. It works perfectly for switching up/down through performance slots (Rigs as well of course).
The only issue is a slight delay when switching between Performance slots. It's small, maybe 1/4 sec, but annoying. Much better than switching between Performance banks of course, but nowhere near the speed of switching between rigs in Browse mode.
Is this supposed to happen? Seems a little odd. EDIT: This was a display delay only, audible delay is not really detectable by me.
Other than that, I am very happy with it! Thank you Paul!