I (ab-)use various other tunes in performing this: for verses 1, 2 and 5 I use approximately the "real" tune; for v3 I use Row On followed by Watching the White Wheat/Bugeilo'r Gwenith Gwyn; and verse 4 starts with the tune of Linden Lea followed by When All Men Sing, with "you'll not keep me from singing" reverting back to the "real" tune in each case.