[CiD]

To bind it to a key you would type into the console something like:
bind <key> toggle cg_3rd_person
where <key> is a valid key like F11 or F12.

Or you could make a file called custom.cfg in you MOHAA/main directory and put the bind in there and it would get run everytime you start the game. If you put the bind in a cfg file then you need to do it like this:
bind <key> "toggle cg_3rd_person"
w/ the quotes and again where <key> is a valid key.

But keep in mind that w/ v1.1 this cvar is cheat protected so this will only work in SP. Also for the people having trouble, another thing to try is in addition to the '+set cheats 1' add '+set thereisnomonkey 1' to the end of your command line shortcut as well. I have heard that is needed as well for cheats to work, but I am not sure.