Key Remapping only when a program is running

[Jagannatha Dasa]

I currently use a script to reassign the tab key to output ` because ` is my global hotkey for Windows Media Player in the WMPKeys program. That program won't let me use tab as a hotkey. My script runs thus:

tab::`

Is there a way to make tab output ` only if Windows Media Player is running?

Thank you very much!