I'm suprised Mecury couldn't handle a print on demand situation for you, unless the volume just isn't that big. I manage a similar digital printing department (Xerox iGen, 2 high speed Kodak B&W presses and a bindery). I've been thinking of ways to set up for my company to automate a print on demand situation for small volume publications.
Have you considered making a digital edition? I may have some resources now that I'm part of the RR Donnelley family now. I'm pretty sure we have a technology where a digital edition can be set up on a site, which can be distributed through email once a person pays. Or it could be up for free if you were inclined.