1. Download VB-Audio Virtual Cable and install it:
http://vb-audio.pagesperso-orange.fr/Cable/

2. Download Autohotkey and install it: http://ahkscript.org/

3. Right-click on your desktop (or wherever) and select "New > Text Document". Change the name of it to something like "toggle [proxmity chat key].ahk". The extension .ahk is important here.

4. Right click your new .ahk file and click "Edit Script". An empty file should open up in Notepad. Paste the following code:

#MaxThreadsPerHotkey 2
[toggle key]:: ;This is the key that will turn the toggle on and off
 t := !t
 if t
  Send {[voice key] down} ; [voice key] should be your assigned proximity voice chat key in PS2
 else
  Send {[voice key] up}
return

5. Edit [voice key] to your proximity voice chat key (or outfit voice chat key if you're a real shitter) and the [toggle key] to the key of your choice.

6. Save and close the file, then double-click the file in the File Explorer. This will start the Autohotkey instance, which you can see running in the icon bar on the bottom right (is that what it's called?).

7. Set up your audio (or video) player to output to "CABLE Input (VB-Audio Virtual Cable)".

8. Open Planetside 2. Go to Settings > Voice > Input Device. Select "Cable Output (VB-Audio Virtual"

9. Play your music, go back to Planetside 2, and then press the key you set up in part # to start your micpspam.

Note: alt-tabbing out of the game will require you to press the hotkey twice to get the held-down behavior working again.