Without buying a new microphone I think the only option would be wiring some kind of switch along the cord, which I'm not sure would turn out too well.

What software are you using your mic with? Are you using the mic for recording using Fraps? Or is it for Ventrillo or Teamspeak? IIRC those have push to talk, or mute buttons, as should most software. What is keeping you from using the software to mute your mic?

I have a cheapo $8 walmart mic that I've used for awhile without problems. When recording I use Audacity to record the mic so I can go back and clean it up later. For live conversations Ventrillo has a push to talk button.

A quick Googleing turned up these:

http://www.crownaudio.com/popless.htm :wiring in a mute button.

http://www.amazon.com/Rolls-MM11-Microphone-Design... :buying a pop-less mute button.