I think the invite only event is a great event- chapters I have worked with do it similar to a pref night.
Also, I would suggest reading "I Heart Recruitment" from phiredup.com They talk about how to get the pnms to let you know if they would accept a bid if you were to extend one.
I know it is hard thought on campuses where all the chapters are COBing and trying to get new members. Something to think about is, if multiple chapters have to cob AFTER formal recruitment to get to total, maybe total is not set at the right level for your campus.
Good luck!
