Just append an ampersand to the commandline, as you would to put any process in the background in shell: perl script params &. Or launch it, hit Ctrl-Z to stop it and return to the shell, and restart it in the background by issuing bg.

If that's on a remote machine and you want to close the connection after starting the process, investigate nohup(1) and/or screen(1).

Makeshifts last the longest.