I don't have a GS-91 handy, but it looks like it does not have that
ratchet release lever normally found on more expensive models ($40 and
up). On the other hand it looks sturdy enough to withstand your attempts
to go all the way to close the handles with a hummer or something of same
nature. Granted, the RG-6 connector is going to be crushed beyond being
usable (it could also be quite OK as I had on occasions), but you could at
least get your tool back. One other way to handle this would be to see if
you can remove one of the pins that hold the moving parts together.
Without actually having the tool in hands, it is rather difficult to judge
if it's even possible with this particular tool.
If you are totally stuck, I bet your next tool will have that ratchet
release lever... :-)