How to make a turnaround without pressurized air in printed parts

Hi,

I'm looking to implement the turnaround idea from many springers into an HPA blaster. I want to use 5/8" OD x 0.058" wall aluminum tubing and I'm struggling to come up with a solution that allows me to add air from the side instead of the back (want to use solid pusher bolt)

Some experiments have shown PETG can withstand ~100psi. Even though a printed turnaround would only see that PSI for a brief moment, I do want to be cautious.

I appreciate any ideas! Thanks.