Flexible superglue...
Strip about an inch off of the smooth backside of one end of the belt leaving the teeth.
Strip the same amount off of the other end of the belt on the tooth side.
Test fit them together and see if you need to remove a tooth or two.
Smear the stripped faces with glue and stick them together. Hold or clamp
until dry.
Some tips:
To strip the belts use a sharp razor blade or x-acto type knife. They tend
to dull pretty fast while cutting through the neoprene. I usually resharpen
the razor blade 4 or 5 times with a whetstone while stripping the belts.
Obviously be careful and watch where your hands are at. If the razor blade slips
or jumps off the belt and hits your off hand it will cut you. (Personal experience :-( )
If you have a scrap piece of belt, use it to help line the ends of the belt up when gluing. It will help with tooth alignment.
For gluing, I use e6000 by goop and clamp the belt together in a vise overnight. Flexible superglue is suppose to work and be quicker. I haven't tried it so I don't know.