Guys, it doesn’t work that way.
I broke some bones in my life, and let me state this:
It is impossible to completely separate the motion of individual bones in a hand.
I understand that this particular bone is still in the area of the palm - given that, as simple thing as just pressing the string with index finger will put a strain on the fracture.
It is not worth it to risk it, seriously. Hands are fragile and complex mechanisms, with so many little bones (that is also a reason why fists are not really all that good weapon in martial arts).
It really would be better to heal the bone first, and then come back to using the fretting hand. Keep in mind also that it will take some recovery time after the casting is taken off.
If OP still wants to play the guitar despite the fracture I would suggest trying out some open tunings like DADGAD together with a slide on index finger.
Not much stress on the bones, as you don’t have to press the strings.