Interesting problem. You can always ask the OS to kill off the process, which could get you where you need to go.
Attached is an example that uses a System Exec call to "killtask" and a notifier to control whether or not that command gets called. I used ping.exe as the sacrificial process since it's easy to keep it going for a user-specified period of time, so the example will only run properly on a machine with a network card. In practice, you can use any process and you could code something similar for Mac or Linux.
I avoided Quit Application.vi from the Windows Utilities suite because that only works if the window isn't minimized, and I suspect most programmatic System Exec calls will want to keep everything hidden.
Take care,
John