I've only ever got in the 'zone' a couple of times... once when I was a junior and once when I was in the bronze medal match at a fita 70m, and was 4 points down with 6 to shoot...
The second time, I got into the zone through 'self-talk' anyone watching me would have thought I was crazy as I was talking quietly to myself, but I finished with a 29, won by a point and was happy

When I was shooting, everything in the background went quiet, and it was just me and the target. The only thing I heard for the last shots was the judge telling me when it was my turn to shoot. The strange thing was it took a while for me to come back out of it... several people apparently told me I'd won, and I didn't notice, and I was in a bit of a daze for a few minutes afterwards!
I guess the key to keeping that for 144 arrows would be by turning it on and off on the shooting line... wandering around in a complete daze for an entire fita might not be a good idea (though those who know me, might think I do that anyhow!)... Unfortunately I've no idea how to do that!
Slightly different, but related really (!) .. I caught some of the Paul McKenna program for losing weight, and he was using a physical thing to control a mental attitude (in this case he was getting the audience to think of a happy situation whilst pressing together their middle finger and thumb). He was trying to help comfort-eaters, so they could get their happy feeling back whenever they wanted, just by pressing together their fingers... Should be able to adapt this to archery and maybe trigger getting into that zone!