As said above, PitchBend is not a regular MIDI CC. They created a separate CC command to get a more continuous frequency change by sending 14-bit data instead of 7. You need MIDI electronics on the pedal to do this. In addition, you would need the pedal to be spring loaded to return to the centre position. The Pedal/Midi Electronics would connect to the MIDI network to send the required pitch bend command strings similar to how some pedal boards work. One company makes such a pedal though (lil' expensive) - beat bars MIDI Expression EX3 . I do not think its spring loaded so I am not sure how you easily get to zero pitch bend. They also have a cheaper Expression pedal to MIDI Pedal.
NB: No I am not affiliated with them. They just came up in the same search I used ti get onto thi ssite.
another method (more versatile than a midi-expression pedal):
"Midi pedal converter" to convert an (any) analog pedal to Midi.
Example: "DoreMidi pedal converter MPC-10" (quite inexpensive, 50-60 usd/euros).
2 analog ins for 2 pedals (e.g. hold+expression, or 2 expression - there's also MPC-20 with 4 inputs)
Can send pitch bend (afair it can simultaneously send up to 4 signals - CCs, pitch-bends, PCs,notes - per pedal)
Bending in just one direction (as the thread owner requested) does not require 'spring adjusted centre position' but just a conventional expression or swell pedal (e.g. cheap M-Audio)
---
Another 'all in one' solution (a de facto standard in guitar world but suprisingly ignored in keyboard world) is Behringer FCB 1010 midi pedal board: 2 expression pedals, 10 foot switches.
en.wikipedia.org
en.wikipedia.org