Friday the 12th isn't much time. I guess first, I would move the date back. Second, I would talk to the people that know your pastor well and see what names they can come up with, also see if the church secretary has any leads on how to get names. If he has kids, you could always ask them to help (that way it would be a surprise for him and his wife, if he's married). I like the idea of a gift certificate (maybe one of the visa ones?) and I would also try to do a scrapbook or a sentimental video or something where people are able to verbalize or write down memories, thank yous, etc.
I've done something similar so email me at ____@____.com . Other factors that would be helpful to know is how big is your church and do you know any of his family?