I would think you could set up a "game plan" with your agency. Let them know you're dossier will be done by May, but you won't have the money to accept a referral until August (for example).
However, I'm sure you'll have to pay all the Agency fees like usual.
Also, some agencies/cases move QUICK - so you'll want to be prepared for the 2nd half of the Foreign fee. Our Foreign fee payments were just 3 months apart
