You can see it in the liner notes of the album here (via link).   From the liner notes:

SINGING BILLY: I don't know how this bunch of words came to be. All of a sudden it was just there. But after I wrote it I realized it needed the voice of the slinky sex to supplemented my own dulcet tones -- so I called on Druscilla Clang (pseudonym, Rosalie Sorrels).

... and

SKIER'S BIBLE SCHOOL: The character of the Old Testament stories have suffered through many and different tales of their activities. I hope they will not mind my pulling them out in the snow. Druscilla helps me with the snow-job.

As for why the pseudonym, I haven't the foggiest. I suppose it's a joke, but as for an explanation, I couldn't say.