What you're referring to is called the Flange. The Flange is used to 'raise' the level of the drain pipe, usually in cases where a new floor has been installed and the pipe needs to be 'raised' too. I could be wrong but adding one won't help the bolts stay in place.
What you might want to think of doing is getting a galvanized washer that's a littel wider than the head of the bolt, and slip it on, then slide it into the anchor hole. This should give added 'rim' to the bolt. For now, you might want to wait and see if anyone else has any other ideas before you try this. Oh, even if you add a flange, you may raise the toilet up too high, where it won't 'sit' properly. So, wait to see what others have to say. If no one else adds any other ides, my idea shouldn't be a total loss.