There is a remote starter engagement wire along the passenger side fender well. Simply disconnect it at the connector just to the passenger side of the blower motor housing and touch the loose end running towards the front bumper to the positive post of the passenger side battery.
Doing so will engage the starter, but not send current anywhere else.
The result? You can purge air out of the system, test your starter, just spin over the motor to get better access to a portion of your serpentine belt or whatnot without ever subjecting your FICM to the lower supply side voltage that will assuredly exist by turning the motor over with the key.
Following the cracking open of the high pressure oil system (to change injectors, work on the high pressure oil pump, change out a dummy plug, etc), we recommend that you put a battery charger on the passenger side battery, let three total minutes of cranking time elapse using this wire (just in 10 second or so bursts with a rest in between, obviously, unless you want to damage your starter), and allow the batteries time to recharge back to full strength BEFORE you hop in the cab and turn the key.
When you DO turn the key, your truck should fire right up and your FICM's health was never jeopardized!