Use cold set rubber product, Sugru, to cover up an unsightly fastener. In my case, it was a screw that was holding up a makeshift whiteboard. I used white Sugru, but any color could do.
Step 1: Make sure that the fastener is not protruding too far out of the wall/object
Step 2: Take a small amount of Sugru and make a ball
Step 3: Press ball into the center of the fastener you are trying to cover
Be sure to not depress the rubber too hard. If you do, just remove it completely and make a ball again. Then proceed with this step.
Step 4: Shape the rubber however you see fit.
In this particular case, I made the rubber rectangular.
Step 5: Allow Sugru to set for 24+ hours before putting any stress on it
Also, take note, this is a "permanent" solution. Do not use Sugru as a temporary cover for a fastener.