I'm not sure how to get them to both start on boot (you'd probably have to edit your boot scripts, which is, in general, not done lightly unless either they're simple, or you wrote them yourself in the first place), but you can get them to both start up on different virtual consoles with, for example:
startx -- :0 vt07 &
startx -- :1 vt08 &
You would replace vt07 and vt08 with two actual virtual consoles that are not in use. On my system, they would be 10 and 12, but that's because I have 8 login consoles (1-8), one running top (9), one normally running X (10), and one running a DC client (11). Most distros only set things up to run 6 consoles and X on the seventh, which means you can use 07 and 08.
Then, Ctrl-Alt-F7 goes to the monitor one, and Ctrl-Alt-F8 goes to the TV one.
This will only work if the card can handle it, though...
Oh yeah, make sure both versions of the config file are in /etc/X11, as well. You can even put all of this in a script, and just run that script in place of startx, if you wanted...