Oooh, I'll lend you my partner... he LOVES calls like this.
He holds the record in our house for keeping a crap caller on the line for 45 minutes.
Examples of his antict; He puts them on hold, asks for a full explanation then asks for it all in writing, asks all the details, puts the phone on the side for a while, picks it up (and they're still there!) and keeps talking, and on and on.

He would say 'um, hang on, let me just get him/her for you, please hold'.
and dissappear for a while.
Other thing is to just put the receiver on the side,keeping their line busy, they can't hang up till you do to free the line.