The group I was with most recently faced this problem with a few shanties... the only advice I can give is what seemed to work with us.

Rather than remain wedded to doing 'full' renditions of all available verses, just cull your favorites out and sing those. By doing this, you can also learn multiple verses and judge the audience response to longer versions of the tune. Don't be afraid to be conservative in how long the song goes, though. Better to serve up and leave the audience panting for more, rather than slog through 105 verses of "Paddy Lay Back" and empty a venue.

M