Could this work?

I haven't gotten my $150 Promotional Gift Certificate from MCI, yet. But I don't want to miss out on this free shipping promotion.

I've already placed an order for a bunch of pre-order DVDs. I know you cannot add promotional gift certificates to existing orders, but would it be possible to use the "battery trick"? Use the $150 gift certificate to order a pack of cheap batteries, then the remainder of the gift certificate would be non-promotional in my account. Could I then apply the leftover balance in my account to my existing DVD order, seeing as it hasn't entered the shipping process?

I know it's possible to apply non-promo gift certificates to an existing order, but what about a balance in your account that doesn't have an actual "code" for you to enter?

Thanks in advance for any help!

When you go to your exsiting order, it has a box to type in the GC code to apply to it. Even if the rest of your $150 is in your account, you won't have a GC code to put in the box. If you type in the code for your promotionsl GC, it would probably still be a promotional code and would probably come up used.

I do not think this will work. Safest route is to cancel the pre-orders and re-order with the promotional coupon.
Promotional coupon value will not show up in your check/gift certificate balance section of your My Account and therefore will not be used for existing orders. The only alternative I see is calling up customer service and see if they are willing to apply the credit for you. They are usually very helpful if you explain your position respectfully.