should be ok...
take the whole pack, plastic case and all, take the dark slide out (that comes in the front of the pack, it will usually eject when you put it in the camera), tape it to the back of your cam, work out your focal length, and shoot.

take the pack off your cam and put it in the instax and it should eject the first frame now that there's no dark slide and the rollers will work like normal - spreading the chems and developing your image...

all the film moving and taping should be done in the dark like, and if you weren't just messing about you could make some sort of back out of a plate holder or something, so you still have a traditional dark slide for attaching it to your cam.

should be possible for sure...

makes me wanna try now