Currently the only way to pre-order is through Apple or a Cell company. All the other smaller mall style retailers will get their pick after it launches I'm sure.
If you would have had TMobile you can open a new line (even a data line works) and that will raise your credit limit on the account. You only have to have the line open for 4 months and then you can cancel that line. It all depends however as you have to pay a $12 fee a month for the line. Honestly saving $50 over the course of 4 months and getting it when you can afford it is a smarter option.
Maybe Sprint can do something similar. Some time ago I broke my phone but I wasn't due for an upgrade and I couldn't wait the weeks it took for the warranty to process. So we opened a second line, turned my primary into a data line (ended up getting an iPad on that line not too long after), and I was able to get a new phone that day. When I received my insurance settlement I used it to pay off the balance of my older phone. If I would have had a backup phone then I could have waited and saved like $40.00 at the time.