A way to "correctly" print double-page spreads?

[Xcellent]

I'm facing (again *sigh*) the issue of Impositioning a document that I worked on. We want to print booklets ourselfs. The document I've set up is a Single A5 page but it has to be printed in binding format (yes all pages are set up in the rule of 4).
Printing a whole spread is not right either. The solution would be Imposition software but some of them are $400 bucks only that work direcly with PDF.

If anyone has a solution that doesn't require changing the order of the pages in .xar that would be great.

Some options in the PDF export regarding Imposition would be nice! It shouldn't be really hard to do:
If you designed your document as a whole spread, internally it exports all single pages and then re-alignes single pages back to a whole spread.
If you designed the document as a single page, merge single pages together on a whole spread in the correct order.
Of course, an error message appears if the page numbers are unequal 4 (rule of 4).