I had to do this earlier this year.
You leave the rubber in the frame.
While it is rigid, there is enough flex in the frame to get the glass in.
What I done was:
Place frame on the floor, standing up.
Put the glass into the correct channel on the bottom of the frame in the centre of the channel.
Stand on the bottom of the frame, with feet either side of the glass and pull up the top of the frame with your hands.
Get a second person to pop the top of the glass into the top channel while you have the top of the frame pulled up.
Use rags to prevent scratching the frame if you dont want it to get scratched.
Hope that makes sense.