FROM THE STORE FAQ:
Can I use Battle.net Balance in combination with approved payment methods to make a purchase?
Although it is not currently possible to make a purchase using Battle.net Balance in combination with other approved payment methods, this may be made available in the future.

----------------
OK Battlenet, It's the future, in fact I remember reading this question way back when Diablo 3 first came out.
It's time that you made this available. Especially since I'd like to purchase Heart of the Swarm.

Here's the deal-
I've got $13 and some change in my battlenet account balance. But since I don't have 39.99 in my battlenet account- I can't use my battlenet balance.
Why can't I use the $13 and just add the remaining 26.99 with a credit card or maybe paypal?

Oh- and before you say - just add funds to your balance- I tried that- and blizzard's fraud team denied it. I happen to live close to the state line and my internet service provider is in WA instead of my home state. So I call customer service and they ask "Where are you?" and I'm like "home" and they are like, well you tried to reload your balance from Washington state. So the fraud team denied the reload. We'll fix that and you can try again... LAME

So now I have to wait days for the purchase to fail, then try it again, then wait days for the purchase to go thru. At this rate the purchase might go thru before HoTS launches. maybe...

So - to sum up:

A) Blizzard needs to provide a way to use your battlenet balance in conjunction with another form of payment (paypal, Credit Card, wooden nickles, seashells, minerals of varying colors and/or vespene gas)

B) Blizzard's fraud team needs to think a little more about where people live and consider that a payment made from the neighboring state, in a city within a 25 mile radius from the person home address is probably not fraud.

Thank you and good day.