How to install Win 7 without optical drive?

I have a system that I built which I, conveniently, did not install an optical drive in as i'd like to keep the case as nice looking as it can and an optical drive will just make it a bit ugly. I also don't want to spend money on an external optical drive as it costs more than it useful especially these days. I was wondering, is there is a way to install Windows 7 on my computer using a usb flash drive/thumb drive?
