Issue Count Constraint over more that one Column

As a Rapid Board Administrator - I want to be able to set issue count constraint over multiple columns - So that I can set WIP for more than one column giving my team intensives to focus their efforts and helping to get stuff into production.

Explanation : When implementing Kanban, I would like to give my team intensives to focus their efforts and helping to get stuff into production, to clear the “Done” column and maximize the flow.

Having issue count constraint over more than one coulmn This will allow to "simulate" sub columns as shown in attached picture and described on page 42 here - http://www.infoq.com/minibooks/kanban-scrum-minibook