This seems to have an interesting relation to the tradition of wassailers and "luck visitors" traditions or The Christmas Mummers (1858). The song We Wish You a Merry Christmas (Roud Folk Song Index #230 and #9681) from the English West Country (Cornwall) was popularized by Arthur Warrell (1883-1939) in 1935. It contains lyrics "We won't go until we get some" in relation to figgy pudding and seems very similar in form to Mari Lwyd songs used to gain access to people's homes and hospitality. An 1830's version of the song had a "cellar full of beer" within the lyrics.

I'm curious if the Roud Folk Song Index includes any Welsh songs or translations that have similar links? Perhaps other folk song indices (Child Ballads?) may provide clues as well?