Looking at the tune I'd guess that they add some instrumental bits between the verses to break the monotony - as you can't do that I'd suggest singing it slower. That might defuse the repetitiveness, but as I haven't heard Shirley and Dolly's Version, I may be talking rubbish - it's just a wild guess.

Whatever you do, forget Shirley's version and get used to singing it by yourself. Concentrate on telling the story, and the musical arrangement will happen by itself, and it'll be all yours.

Incidentally, Ralph Vaughan Williams collected a "Lord Ellenwater" in Cambridgeshire with a totally different tune.

Anahata