Last Page of AR Invoice to get printed in an even page

Hi,

I am developing a custom RTF layout for AR Invoice wherein I have a requirement to group the invoices for each customer and at the end of each customer an envelope page should get printed with the Bill-To address. The envelope page should always get printed in an even page. If a customer group ends in an even page, the odd page should get skipped and the envelope page should print in an even page. Is there a way that I could be done. I basically need to identify whether a page is odd/even in my RTF template.