You can look on the Photopass website or the Photopass Facebook page and see if they have any discounts available.
The biggest discount you missed by not doing the pre-purchase, but that ship has sailed. You might find a free shipping offer, or maybe a % off deal (rarer), but I think that's about it.
Depending on how many photos you actually want from your account, it might be cheaper just to order a few digital downloads vs. the whole CD.