How can I replace the glass over the camera lenses?

Yes, only if you're willing to open up the device which is unfortunately the safest way to replace the glass without damaging the actual camera lenses. If part of the glass is already missing then there's no real need to open the device up. You'll want to chip it out along with the adhesive using a razorblade or a pair of tweezers. You can find the replacements online for a couple bucks. Just note that there is a possibility of the cameras being damaged already if any glass shards found their way to the actual lens.