Hi,
What I have done few times is to re use the paper backing of the 120 film, cartridge and the adhesive tape that holds the film to the paper. Cut a 35 mm film on the same length of a 120 film and position it on the place where you had the original 120 film, then rewind the film on the direction as "unexposed" film. The film should be centered on the paper.
Now you will have 12 exposures on 6x6 format or 16 exposures on 645 and you can use the film backing to count the frames.
Here is a picture taken with color film and developed in conventional lab.
It works really well.
DRZ