Some thoughts….
You might find something like this box could convert your Bluetooth midi from the pedal to usb midi.
See https://www.cme-pro.com/widi-uhost/. I have no experience of the device.
As well as midi, Hauptwerk supports computer keyboards (particular key presses) as controls (you can autodetect HW controls to operate from a computer keyboard). Some users have used old computer keyboards to make low cost controls for Hauptwerk.
If you have a spare midi input you don’t use, you could connect it to a simple switch used with “keyboards” (digital pianos) or guitars or to a second-hand piston.
Iain