That plastic peice connecting the hard tiny hose to the big rubber hose is a check valve, there are two of them, that one and i think there is one behind the battery, check those to see if they are still checking correctly, if they are not it will allow the vacuum in the IWE system to fluctuate with the vacuum coming from the engine, and at high RPMs it can drop to far and allow the IWE actuators to try and engage.
Back to your question in the picture you have you finger on the check valve, you can disconnect the hose on the right side of the check valve, that one comes from the engine. Make sure you plug it off cause if not it will just suck air and might make your engine not run right, but what it will do is not feed vacuum to the system and the system will act like the 4wd is engaged (at the wheels) but it wont, cause you dont have the tranfer case switched. Got it?
On another note, yesterday i was driving with the windows down and i was going up a hill and in high RPMs and i could hear real quick the driver side IWE trying to engage and my stomach just dropped from hearing that after i did all that work on mine a year ago. So anyway, i got home today and grabbed the vacuum guage and started checking everything, actuators checked fine, vacuum at each wheel checked fine, and what i found was when i replaced the check valves i used a three way valve and just plugged off the extra port, well the plug dry rotted and had a crack in it and was letting the vaccum out just enough that is was ok when in lower RPMs, but let the whole system drop when in high RPMs, thank god that was it, after all i did with the system before i was thinking about just driving it off a cliff if i had to mess with the whole system again. So here are a couple pictures the check valve. I put a new better plug on it and it held vacuum, so im good for now!
Pics are a little blurry, but you get the idea.