Not sure if other folks have tried this and not liked it.
My ET-73 came with a small wire clip to hang it from something. I hang that right in the lip of the middle section where you place the lid. Then, I firmly place the lid on the smoker. The wire clip is thin enough to fit between the lid and the side of the middle section. Note, this is not UNDER the lid, it is BESIDE the lid.
When put in this way, it keeps the transmitter sticking out away from the middle section and requires no modifications for mounting. The only hiccup is if you take off the lid. What i do then is make sure both leads are pointed in towards the middle section. This holds the transmitter plastic off the hot metal.
-Matt