It is possible to buy recorders with keys for one-handed use and also recorders where you can twist all the holes around individually (the way you can twist the foot joint on any three-piece recorder) to get all of the holes in good places for you. It is also possible for instrument makers/repairers to add custom keys to any existing instrument. For example you could add a key so that you could use your left little finger to do the work of your right index finger. (Although I have no idea how hard it might be to play that way.)
If you want links I can search some out.
