* Buying copies of your app as gifts (you get 70% back eventually), getting the codes, and sending those. However, gifts are per national App Store, so you have to know the store their Apple ID is associated with in advance. Additionally, you'd probably need a method of payment with a billing address in the countries you wanted to buy gift codes in ...
* Setting the cost of the app to free for 24-48 hours, with advance notification of the app being on the store / when it will be released, plus an email on the day of release with a direct app link for the store. The problem here is dissatisfaction if they "missed it" for some reason (thus the really really really early notification to the backers).
There's obviously an automated gift mechanism of some sort. IGN, Sephora, Starbucks - they all have mechanisms for generating gift codes for non-free apps when they do a giveaway. But I don't know if that mechanism is "pre-purchase a ton of codes" or an on-demand private API Apple has available.
1. Add a low price for the first days, ie: 0,99.
2. Then tell a bunch of your backers that you want to give them 1$ via paypal or similar.
3. As you get responses and the application has been bought jump to the next bunch of packers.
4. Repeat.
5. When finish, raise the price you consider fair.
It will cost you around 30 cents * N. of backers and you will get a bit of traction from some early users thanks to the low price.
When the app is opened, prompt the user to enter a secret code that you've distributed only to Kickstarter backers.
And for non-backers, set up an in-app purchase as an alternative method of unlocking the app.
It's possible though that an app that isn't functional without an unlock code or without making an in-app purchase might violate Apples' rules in some way.