Which way does the foot point, and how far?
If it's at an angle maybe something like this would work...
https://static.evanscycles.com/produ...405-9999-1.jpg
It gives you an adjustable strap the sits diagonal across the pedal. That might hold you in there. (Exercise bike pedals are USUALLY, but not always, normal bike pedals so you could replace the pedals with something more suitable)
You might also fashion a larger pedals thats' perfectly sized to your foot and secure it to the pedal, giving you a custom pedal that's perfect for your foot