I bought the M-Audio EX-P expression pedal and it seems to work just fine with my MIDI Maestro 
There’s some room around the heel where the value doesn’t change, but that shouldn’t be a problem as long as you take that into account 
Even though this works for me it’s not yet the solution to the actual question. So that will have to wait for reply from SS 
Edit: So far I tested only the default Tempo Change. Starting from slow tempo it was quite difficult to get a small change for a faster tempo. I’m not sure if it was more about the pedal compatibility or just Maestro/BeatBuddy 
At least 2 BPM increase is a lot bigger with slow tempo compared to fast tempo 
And it went easily 10 BPM in one go