Hoping I understand the question correctly... but I typically squirt any hot plastic back into the Pyrex leaving a "plug" of plastic in the injector and nozzle. I then inject the whole thing onto the work surface. Once this has cooled a bit it is fairly easy to remove it from the nozzle and put back into the mix for reheating.
This is where an extra nozzle can come in very handy... if I still have more molds to shoot and enough hot plastic, I'll fill the injector again with a fresh nozzle and continue shooting a few more.
