See also: 5 Tips for Making the Best Sangria Ever
I thumbed through my bar books for inspiration. I eventually landed upon one of my favorites, the 1972 Trader Vic's Bartender's Guide, arguably one of the finest books written about tropical drinks. On a dog-eared page was Tahitian Rum Punch for 100.
It fits my criteria perfectly. It's a little bit of a rum sour, but thanks to the inclusion of white wine it's mostly a white sangría. There's a variety of citrus fruit for complexity, and some banana and mint get an overnight soak to provide some subtle undertones. The overnight soak also means that the work on the day of the party will be minimal.
There is, however, one problem with the recipe. I can't fit 100 people in my backyard. At least, not without a shoe horn and guests willing to be friendlier than usual.