If a cold runner is used to gate directly on a part, there is only one way to separate runner and part automatically.
This is by using a pin gate.
The mold needs to have 3 plates in this case and will get more complex.
During design phase of a pin gate it needs to be kept in mind to have the gate height between 0,5mm to 1mm and the gate diameter in between 40%to 80% of the part wall thickness.
This is to make sure the automatic separation will work properly during mold open.