italian vat using fiscal calendar perios as basis for sales vat register

can anybody advise.we want to know how we can address European companies requirement where sales vat register will calculate using fiscal gl period as basis, since our gl calendar follows fiscal period. (ex. april month belongs to this fiscal period 04-APR-2014 up tp 04-MAY-2014). so all transactions in AR,AP, PA with gl date 04-APR-2014 up to 04-MAY-2014 should be considered as april 2014 fiscal period. We expect that sales vat register for april 2014 will capture transactions from 04-APR-2014 up to 04-MAY-2014 since this is our gl fiscal calendar period.

What is happening now is that when sales vat register is ran for spain, it captured only transactions for 01-APR-2014 up to 30-APR-2014 (using the standard calendar not our fiscal calendar)...how do we set tax calendar to look at fiscal calendar?