Posting period authorization for various reasons

Hi,

We want to give authorization for posting periods for variuus users like below:

For April 2009 only i want to give for 10 users.

For May 2009 only we want to give 20 users.

For April, May, June 2009 we need to give 5 users

For June 2009 we need to give rest of 100 users.

We have only posting period variant.

How can we configur this requirement.

Thanks & Regards

Venkat