Is there an alternative to the Flexed Arm Hang at Airborne School?

If you can't do a Pullup you won't pass Airborne School. The Flexed Arm Hang is the bare minimum amount of strength required to pull a slip in a parachute under the very, very best of conditions.

If you are too weak to steer your parachute then you are a danger to others in the sky. You will eventually injure or kill someone because you can't slip away from them. It's best you either get stronger or avoid being Airborne completely so you don't accidentally kill someone.

"The Sky, even more than The Sea, is terribly unforgiving of even the slightest mistake"

Check the website directly from Benning for Airborne School. Pay particular attention to this line:

"This is a safety mitigation measure to ensure students can pull and hold a slip to safely avoid fellow jumpers in the air, obstacles on the ground, and assume a proper prepare to land attitude. The flexed arm hang is a SEPARATE event. The FAH will be conducted on the first day of Airborne School. Students who fail to meet the initial FAH assessment will be re-evaluated the next day. For those students who fail the initial FAH assessment and fail the retest, they will be dropped from the course."

So, based on that statement, I would venture a guess that it is a NO to your question. But don't take my word for it. Call the school house directly to find out for certain.

https://www.benning.army.mil/Infantry/ARTB/1-507th/Airborne/Entrance-Req.html

I do not have any info on this and I have not jumped in 15 years, nor have I ever jumped the new T-11's
But I would encourage you to re-think going to airborne if you are unable to meet that standard. Or work on pull ups to meet the standard. I say this, because the harness is very unforgiving and death is a very real possibility, with severe injury also very possible and minor injury common even among the strongest.