Wouldn’t add velocity.
Only way is to use a midi processor.
@Medaillons apparently wants to trigger samples with his feet.
Well, its possible to trigger OT trigs or a keyboard with your feet…
Possible to randomize slices, and problably make a round robin like trickery (lfo with speed 0).
I don’t know which one would be usefull, but long press and double tap doesn’t seem appropriate for that purpose…
Compromises, always ! 
With Velostat you can make FSR (force sensitive resistor) any size you like. It’s better than piezzo for making drum pads. And a cheap Arduino.
Personnaly I’d buy a Doepfer MBP25 kit. Way easier!
Tested and approved :
Probably the best cheap/simple ratio.
8 octaves, chromatic, ready to play once the midi channel is set. (You may want to select octaves with 2 extra switches).
Control crossfader with the expression pedal !
(With hands I definitely prefer my Hydrasynth Explorer!)
I have an MC6 and I had a KMI Softstep. Both are great but the MC6 is a little more “plug and play” with its standard midi port and 9v power req.
There are more solutions but are you interested in changing patterns that have loops, or just hitting loops? Or just one shots? But recommendations are based on what you want to do. Plus, is there a reason you can’t just use Song Mode?
I might play keys or guitar or sing when I have my OT at a show. Some songs might have 12-16 patterns so it’s not realistic for my to look like I’m trying to tap dance and play other instruments. Plus I have to dedicate two buttons on the mc6 to transport controls. So that song might get song mode. Another song literally has two patterns so I can play that live without song mode and without looking like Fred Astaire.
