If my buddy or any other donator is available, I would switch to their backup and shut my air off. This because the fast-flowing air cools both 1st stage and 2nd stage more and more as it flows, usually making the freeflow worse and worse (bloody fast too). Or at least that's been my experience - of course that could be just because virtually all my freeflow experience is from very cold water and freeflows probably caused by excessive exposure to freezing air temps, or these temps + moisture.
I have learned that a freeflow reg, when shut off and allowed to warm up a minute or 3, will usually work just fine.
Not anything you asked but BTW
Maybe I'm just not used to the norms of how deep people go w/ basic gear in better vis, but I would have been a bit hesitant to go to 100 ft in a buddy pair both diving single tanks. Think about it: if at the end of your planned bottom time something went seriously wrong, forced you two to share air, also delayed your departure upwards for a couple minutes (getting calmed down and squared away) and caused stress that raises your SAC 50% (pretty normal). Would you have had enough gas to make a safe ascent? A single tank used by 2 divers gets empty real fast below 70-80ft.
You did a nice job handling the freeflow with calm + clear thinking. In the end bent on the surface is still better than OOA below the surface. Next time I bet you will be much more aware of your budy's location and proximity