Before I get this party started, I just want to say that no, I don't have an iPhone 5 to absolutely guarantee it'll work in the device, but all that's really involved is some pretty basic math.
In this tutorial, I'll show you how I cut and shaved my Micro SIM down to Nano SIM sized specifications. It's not a 100% 1:1 ratio, but the size is very comparable to what you will find in an official Nano SIM. For that reason I'm feeling pretty confident that it will work with my iPhone 5 next Friday.
Take a look inside for the step-by-step video walkthrough that shows how I converted my Micro SIM card to a Nano sized SIM card.