Just call them up and place your ordere before it arrives to their warehouse.
Without notice of the discount, I called them to see when they should be getting it in and they informed me towards the end of February. They went on to say that if I pre-order it now, it will be discounted 15% and it indeed was.
However, I ended up canceling my order because they charged me for the discounted score which did not include shipping because they "could not determine the cost of shipping without the product physically being there" - wtf? So knowing Lucks and the cost of their shipping, (as well as the time it takes for a package to get from Wisconsin to Northern California) I chose to go with sheetmusicplus since I can pay for 1 to 2 week budget shipping and receive it in a matter of 2 or 3 days since I live close to their warehouse. I am, however, going to purchase the cello part from Luck's once it is available as I think they are the only sheet music retailer that sells individual SE parts.