First off, I would extoll the virtues of using the two sides independently. It's hard to get used to, but it gives you a lot of flexibility to mix and match controls. Also, you (almost) never run into the situation where you can't get to a control because it's on another page. You've always got one of the sides free.
MIDI Designer will also let you work with one big page. Go to
More->Config->Options->One Big Page
you MUST choose a different bank on the right and left side. Therefore the bank selectors at the top of MIDI Designer should say something different on each side, like "1" and "2." That way they access different sets of page.

NOTED: If you want to have a huge crossfader than spans both pages, you cannot... yet. I'm aware of this problem and will work towards solving it at some point in the future. can, see this link.