Here is what I have been planning to do with my WSM/Cajun Bandit.
Mount the Thermometer holder from a Genesis gas grill and use either a Weber dual purpose thermometer or a Tel-Tru Genesis replacement (calibrateable) mounted to the center section. Removable if I want to use a remote probe in place of the thermo!
Mount one just below the grate at each level- much cheaper than aftermarket grommets.
Schematic for the Genesis, http://help.weber.com/schematics/bro...1&model=231001
Thermo holder (#40) is relatively cheap from Weber parts, and a replacement thermo (#39) is @ $13 and a Tel Tru is a few dollars more.