Allowing registered members to soft-delete posts in one forum only?

[Target Practice]

Hey guys, hoping you can help me out with this one - I've done a couple of searches and found nothing, but I'm sure one of you will know the answer.

Basically, I'm thinking of setting up a 'guest forum', where passing guests will be able to pop in and say hi. However, by allowing unregistered posting, I'm obviously opening that forum to a lot of potential spam.
As we're only a small forum at the moment, rather than appoint another moderator, I'd like to be able to give our registered members the ability to 'soft-delete' any spam posts. Obviously I don't want that ability to transfer to all the other forums, just the 'guest' forum. I was hoping this would be able to be sorted through permissions, but I can't see any way of doing it without making all my registered members moderators...

Any thoughts/recommendations?