Run a program after install

I'm trying to find out how I can run a program after the nsis install even if the user doesn't check the box on the finish page.

I've used the following code but for the function to be called I need to select the checkbox.
Run an application shortcut after an install

Is there any way of always running a program when the NSIS installer is closed?

Thanks for any help provided.

Function .OnInstSuccess

  Exec "Program.EXE"

FunctionEnd

This starts the program after an successful installation.
Not needed else i think.

Thanks for the help, that indeed did the trick.