How to fake a connected cellular network?

I have a Japanese carrier SIM-locked smartphone Fujitsu F-01F. The system software update is blocked since there is no carrier network connected.

I want to tamper this so it can let me download the OTA update. Do you guys know what is the component/service on the Android OS which the updating software use to get the current cellular network. If I know about that I can give it a try.

Summon @tewilove. Can you give an advice on this?