Could a similar system to DRS be developed that instead increases downforce at the expense of drag. This could be used by a following car when within 1 second of the car in front for certain corners of the circuit. Ideally, the corners chosen would not be overtaking spots, and the system would just be used to keep the following car close enough that they can then attempt an overtake at a later section of track.
Longer term it is still better to find an aero rules package that makes overtaking easier, but this could be a quick and easy short term solution.