At the extreme risk of starting a big fight, I'll suggest you might take a look at getting shorter crank arms. 165mm are what I use and they allow me to get more aero comfortably. Possibly the shorter cranks will not require as much range of motion for your knee.
However, with a pending knee replacement, you might find out that you wish you'd had it replaced years ago. My brother-in-law recently had one replaced after years of putting up with the pain and that's what he wishes he'd done. Though he doesn't cycle, so I've no reference for that.