You could always just put the optical drive back into the machine if you need to re-install windows....
If the drive is modular, you can remove it and put a modular battery or modular hard drive into it's place or just a weight-saving module. If not, you might have a harder time. Also, don't Lenovos come with a recovery partition on the hard drive that lets you choose what parts of the original factory install you want to restore to the main drive (I think this is a feature, I saw mention of it over on the forum at NotebookReview.com)?
You might not be able to use a USB drive to install Windows since it might require pre-installation drivers that you wouldn't be able to provide. If you remember with XP and SATA drivers, they could only be installed in 2 ways - slipstreaming it into the XP CD or using a floppy drive; it could be the same way here.