If you have a printer with opens belts (like I have) You can use these to clamp both ends of the gt2 belt together.
There's a 3 mm hole in the center for connecting it if requiered.
1) print the clamp
2) slide the clamp on the belt and see if it's a good fit (else try offset)
3) cut the belt to desired length
4) glue the belt in place with some superglue