The linux kernel team set something up that they are pretty happy with. I don't know the details, but they have dealt with the influx and feel comfortable their solution will last.

https://www.youtube.com/watch?v=NnV_cWeoo5Q

One thing I've been thinking is something like the DCO checks. Set up some account bridge between (eg.) Discord and GitHub, then auto close anything submitted by accounts not sufficiently involved with a message linking to the new contributor policy and rationale.