Don't!
I answer questions in part because the research and writing practice is useful to me but the main reason I answer is to help the people who ask. If you already have an answer but want more possible answers, by all means post then answer your own question. There are even badges for that. But if you don't actually care about the answer and just want more traffic, don't. Just don't.
I was on a low volume mailing list once that I enjoyed. Then the listowner kept posting weird provocative questions and I spent a long time answering them. I finally realized I was being baited. He confirmed it. He asked questions specifically to upset me in a way that got me to post, all to increase traffic.
It completely backfired. I just left.
While you're not targeting a specific person, you're talking about posting for the sake of posting. It's one thing to seed a group with a few choice questions to get it going. But that's not necessary here. We get a bunch of questions every day. You'd be doing this for the numbers.
So please, post questions you honestly want answers to. Don't turn this group into a game where people never know if the question is real.