automatic page duplication within multilateral documents to prepare imposing

Sometimes i have multilateral documents which have to be imposed like this: 2 sets per sheet where each set has 4 pages (2 front - 2 back). So when i impose a multilateral A5 document on an A3 sheet with double sided printing and i cut it in half i'd like to get 2 multilateral staples with 4 pages on a sheet. To do this i have to duplicate each side once to impose it right.

Tried it with shuffe (althoug i have 50+ pages) but it won't do the job - it sets the wrong pages on the back ( 5,6 on the bacl of 1,2?! - what did i wrong)

I can provie a PDF toclarify my idea - it may be confusing