I faced this same issue on the Ford, and now that I have Pacific Dualies wheel liners on my Chevy, it's a similar situation.
Here's what I've done:
First, the kit:
compressor, double foot straight gauge, valve extender, 11/32nds hose
I've installed these short extensions on both motorhomes now, neither has been an issue over the years. I tightened them to the original valve stem with tiny adjustable slip-joint pliers when I installed them, and to date, never had a leak:
For the inner dual: peering through that "handhole" that some Ford "engineer" should have had their head examined....:
Simply use the 11/32nds hose to reach in and remove the cap:
Result:
Reach in with your double-foot gauge to check the pressure:
If you do need to add air, use one of those dastardly extensions attached to the inner dual shrader. The female end of the hose is fixed - it will not rotate independent of the hose. Thus, it can be installed by twisting the hose:
Attach your compressor:
It helps to have a screw on fitting, where the push-on style is difficult when holding the push-on to the hose, and turning on the compressor. two people (or three hands....) would be helpful. One of the push-on type with the hold clip would help, or having a large compressor that has a holding tank.
This setup would work on the sprinter as well.