if someone would give you a million dollar to get on a plane without going through immigration( in a asian airport), How would you manage to enter the secured area?
You will have a ticket and passport but will not be allowed to go through immigration and you would receive the money only if you managed by your own ingenuity, to fly out without being stopped/detected. You will know only the gate number that your flight departs from and a map of the airport.

If this would be even possible (personally I don't think so), How would you plan it and which methods could be used?

if you where caught there would be no punishment.