Since you asked for our opinions...
I am totaly against adding temp holes for the last night. The last thing anyone wants is to lose to another team on some made-up hole the last night of league that they had never gotten a chance to play before. I know they do it in tournaments and I don't like that either, but that's a different discussion (like maybe limiting the field in tournaments instead). Also, I would hope you wouldn't use your basket for one of those holes. I have the exact same one and it sucks for anything but putting practice.
Note: for at least this summer league, there will be 2 teams not playing the last week (Andy/Doug and Chris/Jim) because of food preperations, etc. Not that 4 people makes much of a difference, but it's a little help.
Maybe while people are waiting at a hole to tee off they could be picking up cigarette butts and trash and you can give a prize for who brings in the most trash, haha (no bringing trash from work Link).