Rigging a 100-page book, I need your help

[naek_spartan]

Hey CG pro's, I need help on rigging a book. I already wired one page rotation on a dummy. And added a roll parameter(0 to 100) to the dummy object. I just want to add an expression so that the page will start rotating when it reaches the value 20. So if I do that, then i can let the parameter control a 100 pages. For example: page1(0-20), page2(20-40), page3(40-60),....and so on.
So the pages will rotate on turns right. The dummy holds the attributes(i added an attribute holder modifier). And 1 roll parameter. That means when i finish a 100-page book i just roll the parameter and the pages turn, you know?.

Or maybe you guys have another idea how to rig a book. But i just need an expression.

Thanks a million...