A flag to allow posts to your thread beyond the normal necro date?

I have a writing thread that I accept prompts on. Sometimes the thread doesn't get much traffic and I don't post much to it, busy with my other content (or life in general), so it slips into the necro zone.

Just a couple of hours ago, someone PMed me asking if I was still taking prompts. I said I was, and asked them to post it to my thread. They did so, and got reported for necroing. I'd like to avoid something like that happening in the future, if possible, and a sort of flag you can set for the thread would be excellent.

 

I feel like saying something in the first post (maybe a status line?) or acknowledging the necro-ing prompt ought to do it? In particular, if you respond to a prompt even just to say "yes, I received your prompt", that tells the mods "I, the thread OP/nominal author, consider this to be on-topic and on purpose for this thread". Which I think they usually take into account. (It also implies to non-mods "don't bother reporting that".)

 

The thing is, I did that, and this person still got a mod slapdown before I arrived to say so. I don't want this to be an issue if I'm not there to give approval immediately.