IRI instrument - Settlement date for interest

Hi SAP Gurus

I want to settle the interest payment on the 5th working day of every quarter but the calculation is for each quarter. How will I be able to do this?

I tried using the 'Manual input' for frequency & input the frequency as 3 months & I set the period end as '09302011' & due date as '10072011' but for the next quarter, it just shows as a 3 month shift. Is there a way?

Thanks

Regards

Morgan