My suggestion: 5 laps or less in a race = automatic time penalty.
Every other scenario (using Vettel v. Hamilton to simplify the explanation):
Vettel is told by the stewards to allow Hamilton to pass by the time he hits the start/finish line. Vettel must remain behind Hamilton for one complete lap. Once that lap is complete, Vettel would be free to race Hamilton.
Think of it as a modified virtual safety car for 2 competitors.