Sadly I don't think you can stall that third common. The ai needs the first 3, sometimes 4, Commons of each realm just to be competent.
As long as ai can roll only 4 books in their main realm (happens regularly with myrran AI), you can't stall it.
As long as ai can roll only 4 books in their main realm (happens regularly with myrran AI), you can't stall it.