I did some searching at for and found that you could do this:
I decided to use two button bindings, one for portrait mode so I have access to keyboard and other on-screen controls, another second binding for setting the screen mode to landscape when time to play.
bind aux1 "vid_mode 0" // normal portrait mode.
bind aux2 "vid_mode 1" // landscape mode (RIGHT) 320x240!
I found this setup to be most efficient.