[whpalmer4]

Are you asking for an option that simply stops OmniFocus from trying to sync over a 3G connection, but continues to let it sync automatically when connected to the internet via WiFi? There is already a WiFi-only sync option, if you are using OmniFocus for Mac, but you can only use it when OmniFocus for Mac is running, and the Mac on which it is running is connected to the same WiFi network as your iOS device.