Bottom line is there is no easy way to produce this. You don't have A5 paper and will need to cut A4 in the middle after printing on both sides. The biggest trick is working out how the spreads align and what goes on the back of each pair.

For starters, you need a pagecount multiple of 4 so your ~30 pages needs to be either 28 or 32.

Then your (2 page) spreads page order should be in pairs which need to add to x+1 with the odd number always on the right. eg for 32 pages the facing pairs are 32,1 on the back is 2,31; 30,3 on the back is 3,29 etc. To do this to A6 size you print that sheet's page order as 32,1,30,3,2,31,3,29 as 4up double sided - flipping on long edge.

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Andrew Lockton
Chrysalis Design, Melbourne Australia