I have always sung "When I Was One and Twenty" to the tune of "When Irish Eyes Are Smiling". It fits just right.
Another idea is to sing Marlowe's "The Passionate Shepherd to his Love" (The one that starts out with, "Come live with me and be my love...) to the tune of "I'll Take You Home Again, Kathleen"
I love poetry which, in my crowd, makes me stand out like a bagpipe in a bluegrass band.