On a UNIX system you can run the remote process in the background by appending "&" to the command. For example, if I have a utility called "/my/bin/a.out" and I want to run it on a file called "xxx" I do this: system '/my/bin/a.out xxx &'. Not too familiar with MacOSX but I believe it is UNIX based is it not?
On my PC, I use the Win32::Process module. It also allows you to run a process in the background. Perhaps there is a MacOS equivalent.