Keyfigure values in BEx Report

Hi,

I am working on a BEx Report which shows the keyfigure amount for a span of one year from jan to Dec if run for a calendar year. The requirement is that if the report is run in the month of october the Amount displayed for November and December should be the same as october value and similarly if the report is run in the month of September the Amount displayed for Oct, nov, dec should have september value. Could any one of you suggest if you have solution for this kind of requirement.

Thanks

Raju