On the line coming right off the intake, about half way between the intake and the soleniod is a check valve. Disconnect the hose from the check valve, on the side of the check valve going to the solenoid. Now you need a cap to cap off the check valve. The cap keeps the engine from sucking in air all the time (You dont want that) and unplugging the line repleases the vacuum from the IWE system and allows the hubs to engage. This is fine because there is no grinding to harm anything. You are not in 4WD at this point. all your axles up front will turn cause they are engaged, at the wheels but not at the transfer case. The only thing you will notice is maybe a slight loss in MPG.
This method stilll allows you to engage into 4WD if needed. Because your front axles are already engage. When you turn your 4WD switch on the dash or shifter on the floor the transfer case will then engage to the axles and give you 4WD.
I try not to ramble to much, but does that make sense?
2012 F-150 XLT 4x4 EcoBeast SuperCrew
2007 F-150 XLT 4x4 5.4 SuperCrew - Leveling Kit - Magnaflow Cat Back - Tonneau cover - Traded
2004 F-150 4x4 S-Cab, 4.6, Auto, Edge Programmer - Traded
Everything You Wanted To Know About IWE's