Assuming the VPN startup uses stdin/stdout, you can use the Expect module to converse with it. To background it, you can send it the STOP signal: kill $SIG{STOP}, $pid; To have it continue send the CONT signal: kill $SIG{CONT},$pid;. You can get the pid from the spawn method of expect. Or, you could issue the ^Z/bg commands via Expect, which sounds simpler, on reflection.

As to knowing whether it has succeeded or not, you probably need to come up with a test based on the ability to connect to a VPN protected resource, like the DNS servers for instance.

Update: Doing job control with Expect will only work if the command you spawn is a shell with job control, and not the VPN command itself. So you would spawn the shell, and then exec the VPN command with a send to the shell. It may not be simpler to do this compared to spawning the VPN command itself.