Maybe a dumb question but...

This is just my guess, but i don't think the fan design would allow to to physically build any pressure.
With how far apart the blades are, I'm almost certain that any extra pressure would just slip past them. Cause it's not about how much air it can push, it needs to be able to to act as a one way barrier. It's always worth doing an experiment though :)

Just find someone with a plastic weld and build a housing in front of the fan, seal it off, and drill/thread a hole for a psi gauge.