Then build the customization into the product, also, are you sure they really want to spend three hours with you? Can you not do the Henry Ford method of any color as long as it's black?
If the customization is purely the skin, then create a system for skinning, and get local designers to make skins. Then create a market place for them, and hire a bunch of people to make skins. (I assume it's skinning b/c your a graphic designer).
As an aside:
I used to do custom wordpress themes but stopped because it was so much easier to have nice printed themes. Walk into the client with nice glosssy prints. I could buy the theme for $35 bux and resell for much more rather than deal with the nuances of the customer. Most customers just want it to look like some other guy's site anyway so why not provide that?
They actually would pay more for a standard theme because I could turn it around faster, and they were happier because it looked like everyone else's site. As a designer I never understood herd mentality, as a business man, I love it.