Batching-Center into paper

Hi

When I send a batch with a 3 documents with JDF 

- document 1 size 700x500 mm

- document 2 size 710x510 mm

-document 3 size  730x520 mm

The final document size its 730x520mm but smaller documents align to left.

Can I center documents into a paper with JDF?

What its instructions to do this?

Thanks for all

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