Simplest thing would be to just not post in it, as you said. Others could still bump it, but it's really not a huge deal. If you really want one of your threads closed, you could potentially PM a staff member and ask.
You can request it to be closed by report it, saying as the title says. Then a member of staff can get to it and they'll close it for you.
Also, you can just leave it alone. It's no matter if it's locked or not.
