What if you taper (reduce the diameter) of the male fitting and use it
to mark another male fitting.
If it has a stamp or mold marking on the male...mark it from there to
the female. Then use a new one that will fit tightly!
That's similar to what Existential Angst wrote above which was,
"If worse comes to worse, pvc fittings are not that expensive, so maybe you
can just remove some material from them so they can rotate, and sacrifice
them for this particular app, and have spares on hand.
Keep them around for future fit-ups, but mark them so you don't
inadvertently use them."
But, your idea is a little more specific about maybe just reducing the size
of a test male fitting to do the line-up. In my case, that probably would
have worked more easily than what I ended up doing -- which was basically
using brute force and some leverage.