Good question. Let's say that you can start a backup, but you'll need to record them as follows:
Actual NFL starts (your starts)
So if you're starting a guy for three games who didn't have any NFL starts, you would denote him as 0 (3). That'll let us know that you're pressing a backup into a starting role, but it's better than starting a scrub.
My ancestors fought cave bears so I could make this post.