hmm that is a hard one
a ****tail wedding will be formal attire i guess
maybe could get away with a easy to access top under a geogous jacket- or even use a shawl for effect that can double as a cammoflarge when you are feeding.

can you ring and speak to the venue to see if there are feeding faciliities or there is somewhere you can go to be discreet- that may help you decide how much you need to keep covered or you can just let it all hang out-lol
goodluck and enjoy!

odette