I think you're underestimating how hard it would be to strangle an armed and armoured guard... also, that requires him to already be holding the keys, not just have them on his person.

Rather than strangling, which seems like a longshot at best (keep in mind that Command doesn't leave them helpless, they could still fight back) you'd be better off making a prison shank (Sujurak could help carve you one using his claws). Lure the guard over by feigning sickness, cast magic weapon on the shank, and try to stab the guard to death. Might get a bonus of him being flat footed or something if you're lucky.

This has the advantage of not relying on the guard failing his saving throws and leaving you exposed as a dangerous caster if it fails- if it looks like you're having a hard time with the guard, you can always try to pull the keys off him and throw them into one of our cells, forcing him to either rush over to stop us letting ourselves out and giving you a chance to shank him in the back as he turns to deal with the new threat, or else he can ignore it and soon have more people attacking him.