[Closed] Anyone use pedal extenders with allen key only pedals?

Trying to resolve some niggling knee pain that's keeping me off the bike. Had a bike fit which suggested the issue is mostly with my twisted pelvis and crooked back! Came away with lots of exercises and the suggestion that pedal extenders might also help.

They range in price from £15 to £50. £50 gets you a set drilled for fitting pedals with 8mm allen key sockets, but that gets a bit spendy over two bikes!

Heard a rumour that you  could grind spanner flats onto the pedal (on the shoulders where the flats would normally be but aren't on a high end pedal) but this sounds a bit bodgy. Anyone tried this?