So what makes a bagel, a bagel?

I've got the Bread Baker's Apprentice, and love making the bagels from it. They're always a big hit at work :)

I'd like to make some different kinds of bagels, like rye or pumpernickel. Does anyone know what (if anything) I'd need to do to my regular rye/pumpernickel formulas to make them work for bagels?

Thanks!

-Joe