How many drives do you really need?
Those two xdock slots are designed to be easy in easy out, so if you really needed more space for 3.5's you could always just pull one out and swap it in a few seconds.
But if u really need more than 2 3.5" drives installed perm, them modding the case is possible, there is plenty of room downstairs for that.
But the way I see it, buy a case that fits your needs either right out of the box, or easy to get it the way you need it. Buying a case and then trying to install a build into it that it just wasn't design for isn't a good idea.