This actually shouldn't be a very hard mod. You just need to find the positive and negative voltage ends then wire up a 2 pole mic to those prongs. If you want to make the mic removeable, then get yourself a mini-stereo plug (both male and female ends) then wire it up the same way.
If you go the mini-stereo plug route, then let me suggest that you use a powered lapel mic. I switched over to using that just before SDCC last year, and although the mic was like $25 it was a great investment. I'm still running on the same battery I bought it with, and It's pretty loud.