Er I'm not really seeing what the big deal is here. We do impositions with items facing different ways often enough, to get more on the sheet. Also not uncommon to run a job a few percent smaller, customer never notices. Seriously though, it can't be that much of an issue unless you've already quoted it 4up, if not, then what's the problem?
3 up dutch cut is the answer to the original question, as most people have noted. Not a big deal.
However, when the runs are short, which they often are, I'll sometimes throw them on the sheet two up, right down the middle and slam it out. (You can also move it around to avoid print flaws if necessary) The cost of paper is negligible, and if all you have for imposition is what came with the 5500, it's a fast and easy template.