I wonder if your wheel simulator is properly "clocked". One of the openings has an extra, small, cutout that allows easier access to the valve stem. My RV has a standard rubber stem and it's easy to reach with a regular angled pressure gage and filler (although it probably would be difficult to reach with a "round" inflator).
As others have offered, there are some good 90 and 45 degree metal extenders that will do the trick for you.
Coyle & Sue
Cassity (Labrador) and Rylee (Standard Poodle)
2007 Damon Challenger 355; 2003 Element toad