Interference Pop Foul First Base?

[TwoBits]

Speaking NFHS rules, I think you have interference here, the runner is out, batter returns to hit:

Casebook 8.6.10E: R1 on third and R2 on first. B5 hits a fould fly ball near the third base line (a) with less than two outs or (b) with two outs. R1 interferes with F5 who attempts to catch the foul ball. RULING: in both a and b, the ball is dead immediately and R1 is called out for interference. Additionally, in (a), R2 must return to the last base touched at the time of the interference and B5 is charged with a foul ball.

Yes, there are a couple of differences with this play and the OP: first base side versus third base side (which I doubt makes a difference) and runner on base versus off base. However, after combing through the rules and case book, I don't see an exception for a runner being exempt from interference while on base except if it was an infield fly situation or if the batter is struck by a batter ball. In this case, neither applies, so I think you have to call the out and prepare for an unhappy coach.