Lets say you've decided on a $600 annual FSA account. Create an asset
account (in your case a credit card account) with a $600 balance and a
liability account with
a $600 balance. Your monthly payroll fsa transfers reduce the
liability, reimbursements reduce the asset. This correctly reflects
your fsa status since reimbursements are not limited to your to-date
deposits. At plan-end (you can submit claims for a year for some weeks
in the next year - your plan adm. can tell you the details) write off
any remaining balance in the asset account. Start next year with a new
$600 asset and $600 liability.