Ah, I fell victim to the same thing! Bought the Adafruit jack and it won't fit through the 5/16" hole. Bought a pack of these: http://www.amazon.com/Generic-Barrel-5-5x2-1mm-Pan...Now I can build 9 more ISS-Overheads, which is probably going to be necessary when my coworkers encounter mine on my desk.
Impower - The (Electric Imp powered) Internet Connected AC Outlet
Getting Started with Electric Imp
Electric Imp Garage Door Opener
Internet Enabled Solar Tracker
IMP-ERSONATOR: Electric Imp + Arduino + Wave Shield = Remote Sound File Player