Workflow for eBook and Litho printing

Thanks to the input I've received from the forum, I have the CMYK workflow for sending a PDF off to the press for litho printing.

But what if the client wants an eBook as well as a printed book?  So that's an RGB document.  I guess I could convert the CMYK PDF to RGB, but that's a double conversion of the images, right?

What's the best way to produce both types of books, starting off with RGB?

Thanks in advance.