If you use a HV supply (> 200V), feeding a 10K resistor to the collector of a high voltage transistor and connect this point via a capacitor to your aerial, I can't see why it should not work, providing you only switch the transistor on when the RF is off.
In the early days of radar, a neon tube was used, one end connected to the line, the other end was then pulsed to make the neon strike and short the line, but I doubt if you could make it any faster then your 600 micro secs, still you could have a go?
Frank