I have many hours showing retards how to use technique to avoid runs. Usually it is a disaster...and we spend more time fixing the "repairs" than working on technique.

Do what you are doing with the razor,(if you have atleast 2 wet coats of clear),then hit them with a rubber block and 600 paper WET. You have to pay close attention to the OUTSIDE area of the run(s),they WILL go through first(less material).Make a few passes,feel it,if it is coming down move to 800,then 1500 then 2K. It is a gradual and slow process,but I have been successful at it scores of times this way without breaking the clear,though it has happened. But only about 10% of the time.
Also try to use a synthetic compound,as it wont take as much down as typical compound will.This is where you usually go through,the buffing part. Syntheticut works awesome for this kind of repair.
Good luck