Errors when WBS closed before payroll posts

Dear Experts, we are having issues when employees post time to a WBS or IO which are open at the time - but are closed before the manager approves, or before payroll posts.

We post weekly, so the employee may enter for 4/26/11 when the WBS is still ok to post to -but it is closed on 4/27/11 to prevent future postings going forward. We still need to post the 4/26/11 as it is valid for that cost object. WE don't see anyway to use validity dates for IO or projects. Any advise?