Is it possible to run the script as a daemon?
Well, technically it's possible to have a script exit CHDK <ALT> mode and run while the camera is in "normal" operations mode. The script can also re-enter <ALT> mode. See exit_alt()
Here's a simplistic example :
draw_string(50, 50, i , 257, 258, 2)
But as reyalp will be quick to point out, that's a mode where the script and camera behavior is somewhat undefined. So you would have to try that at your own risk.