Hi, I am from Bangladesh. I need to get G visa for transit in Hong Kong International Airport.

I will go to Boston(USA) from Dhaka Airport via Hong Kong International Airport. I have not get my F1 VISA from the US embassy yet. Hope I will get it by 20th to 22th August but I have to fly in between 25th to 27th August. Can I apply for transit visa of Hong Kong (G visa) before getting a F1 VISA of USA? My travelling airlines will be American Airlines. But for Dhaka to Hong Kong it will be operated by Cathay Dragon. Hong kong to USA it will be operated by American Airlines.