Upload & Sell: Off
I did one this summer that worked out pretty perfectly.
The couple were going to have a small wedding (second marriage for both and they both had children) but that they wanted to have a nice engagement party. They ended up having a beautiful engagement party and it just so happened that the grooms brother was a wedding officiant, so towards the end the groom was giving a toast thanking everyone for coming and suggested that since everyone who was important in their life was already there, why not go ahead and get married. Obviously, this was planned out ahead of time, but only me and about two others knew. It was really pretty awesome and super fun to be a part of.
The only thing I might suggest to your friend would be to try and figure out a way to do it at the BBQ if at all possible instead of City Hall because by far the best part was everyone's reaction when they made the announcement.
I'm not much of a poster on FM and have never linked a picture, but I'll go ahead and attempt.... Here is a picture of the mother of the bride right when she found out. (Apologies if this doesn't link correctly...)