Anywhere near the exhaust and most importantly OUTSIDE the slipstream will be fine. This is what I ran with yesterday:
It is a Rode Video Mic Go, which takes its power from the camera (GoPro HD2 in my case). It is directional, so I point it down.
Here is the result:
Note that before 0:45 of the video, I forgot to put on the "muff", and I guess the exhaust is so loud now that the mic got "blown"
Exhaust setup is Borla S-Type Mufflers + Borla X-Pipes / Mid-Pipes + secondary cats deleted.