How to defer Travel advance until two weeks prior to travel date

We provide Travel Advances (using PR05 via FI module) for our employees but would like to know if it is possible to setup a trip that is several months in the future but not have the 'advance' posted until two weeks prior to the actual trip 'from' date.

If this is possible, can you supply steps on how to make this happen.

I tried using the 'advance' screen and future dating the advance amount but that doesn't seem to do anything.

thanks

Linda S.