FAST makes an adapter that you can insert into the tail pipe and clamp down (others may as well). It just holds the O2 sensor so it would work for any tuner not just the FAST systerm.
A number of vendors make a short section of pipe with a bung in it, if your exhaust is new enough you can disasemble a straight section, slide the sensor pipe in and clamp it all back together. If your car is like mine the exhaust is fused solid and cutting it would be the only option.
I've done some tuning of mine using the tail pipe method but the chrome tips don't lend themselves to using the clamp so I really can't road test it which will give you better results. Also, ideally, you want the sensors further up the system, especially if the pipes mix, that allows you to tune left and right individually to get the mix just right, my FAST meter supports 2 sensors for just such tuning. You can do it with 1 sensor but you'll need to move it from side to side (which can be hairy as the exhaust pipes tend to be hot).
