I know you aren't the one determining "what" the shipping configuration is, however, you may want to find out the logic behind why they wouldn't offer free shipping on more than the first order.
Seems to me that if they plan on growing sales they should keep the customers that have already purchased from them (meaning they are "willing to buy!") happy so they come back. Offering free shipping on orders to them would help with that regard.
You need to keep a base if you want to increase overall sales. The base (or foundation) should be those customers that have bought. Again, they may have some logic to it, but I can't see how it would help. I can see how it would hurt though.
Why not do this. INSTEAD of creating a "Discount" coupon, clone the "flat shipping", or "free shipping" module into a new one. That new one would offer free shipping (with conditions you specify). That way, you could run a query on the DB upon account creation and either show or "hide" the free shipping offer based on the results (see next paragraph for more on that).
You could run a query on the DB and check to see if the users email addy is already present (upon account creation). Then, run and "if then" based on the results found. (IF record was found THEN bypass the discount ELSE, give the discount). I am doing something similar on an old version of zen (the only way to do it then).
I did this and created a new shipping method called "promo". I cloned an existing shipping method and then altered to fit my needs. Then I promoted "Free Shipping" with the first order on the site. There was no discount they had to enter, but rather, when they got to the "shipping" section of the checkout (or shipping estimate), they were presented with a note saying they qualified for free shipping (and the "free shipping" radio button was shown to them).
Seems like that same tactic would work for you. If I were in your shoes though, I would recommend letting them in on the "drawbacks" of free shipping ONLY on the first order (for repeat sales reasons).




