Can't give you definitive answer - but - often with scoots that have the seat open w/ key at the ignition switch you can access the cable at the switch. Depends on whether you can remove enough of the front panels to gain access to the switch assy.
If you can get at it, you may be able to be able to figure out how to pull the inner cable to release the seat latch.
If something is caught in the latch, perhaps using the key to unlock and pulling up hard on the seat will pop it open.
Good luck!