Obviously this only worked with an old version on the 3902 platform, I can't remember which version exactly. It was a little more complicated than you describe though. Here is how it worked:
1. Locate a Game King video poker machine configured for multi-denomination play.
2. Make sure the Double Up option is enabled on the machine.
3. Insert money or a voucher and select the lowest denomination level offered by the machine—for example, $1 per credit on a $1, $2, $5, $10 machine.
4. Choose your favorite game variant—Triple Double Bonus Poker is fun—and start playing.
5. Keep playing at the $1 level until you win a big hand. An $800 royal flush is perfect.
6. With your royal flush showing but not yet cashed out, hit the More Games button on the touchscreen and select a different game variation. Play it until you score a win.
7. Insert more money or a voucher into the machine.
8. Touch the More Games button again, and change to the maximum denomination—in this case, $10 per credit. Then return to your original $800 royal flush.
9. Press the Cash Out button. “Jackpot! $8,000” will appear on the screen and the light on the top of the machine will illuminate. Congratulations!