You are a wide-eyed optimist.

Putting aside, for the moment, that previous, similar petitions have failed, I'll explain why your idea won't work.
In the most recent
popularity poll,
Monkey Island came in a distant third. And that is after Foul_Smelling_Pirate and others voted multiple times. The thing is, people are willing to vote or sign a petition numerous times but they are not willing to buy numerous copies of the game. This is why LucasArts ignores petitions and polls. They are not a true reflection of the market.
Further, the belief that 1000 signatures (even if none are duplicates) is "all you need" is completely false. It is no where near what you'll need unless those 1000 people are willing to spend $1,500 per game. Remember that LA shipped 35,000 copies of EfMI in the first year and those were considered mediocre sales. So, to make LA stand up and take notice, you'd need at least 75,000 signatures or better.
If you think you can get 75,000-100,000 unrepeated signatures in your petition, more power to you. I seriously doubt you will find that many people considering how the previous petition attempts fell well short of that number.
It would help if you get $30 per signature as a down-payment for the next game, pursuant to a contract with LA, stating that each signatory receive a coupon guaranteeing them a $30 trade-in on LucasArts products. If you get 75,000 signatures, then LA will get $2-3 million to cover their overhead in the creation of a 5th game. They will be guaranteed a profit and the signes are guaranteed a
prepaid 5th game.
So, I suggest that you put all your optimistic energy into contracting with LA and creating a pay-per-sign petition. This will let LA know all signes are truly serious.