First of all, credit goes to DJ Foam for figuring out how to do this with any vehicle, I'm hoping someone will make a video so he can add it to his vehicle list. I will add pictures later, here is how it goes

First of all, manage to land your jet near your apartment and take it to your garage before proceeding.

1. Station the jet so that the tip is touching the right corner of the garage, make sure there is very little room to the right of the garage (enough to fit but not to be able to get on the jet). This makes it so you teleport inside the jet (like the tank).
2. Call anybody that can give a job and wait for the job request menu to appear, keep the menu open.
3. With the menu open, go to the right edge of the garage (the little area left by the jet).
4. First off, test to see if it works, press y, in approximately 2.2 seconds you will spawn inside the jet, if you do teleport inside than you can do this the same way with the tank.
5. Get off if you got inside, and do the same thing, except this time you will time yourself. Remember to face the garage (this enables you to get in when non in some sort of menu. Press y, and as soon as you think you are close to 2.2 seconds cancel out the job request menu.
6. I tried it a few times so the first time might not work for you either. It is a good idea to grab some sort of timer (I used my ipod), as the time has to be around .1-.2 seconds away when you exit the request job menu before teleporting into the fighter jet. If you get teleport inside the jet, and it automatically makes you get off to go inside your garage, simply reposition your jet.

HOW TO INSURE
1. Grab any vehicle in your garage that isn't the jet and exit the garage.
2. Exit your vehicle and destroy it.
3. Renter your garage and get on the Fighter Jet (BUT DO NOT MOVE IT, STAY INSIDE THE GARAGE)
4. Call the insurance company, and whatever insured vehicle you had destroyed will appear. DO NOT GET IT BACK
5. Exit the garage with the fighter jet, during the garage leaving animation you will still have the option to pay for your vehicle, do it during the animation.
6. Since the fighter jet is so big, either two things will happen, it will explode, or will be teleported outside with fire coming out of its engine, you want the latter obvously. If it does explode go to online > Find New Session. After that you can go into your own lobby again and redo the process.
7. If the Jet is teleported outside (on fire) then simply do the glitch again, (Steps 1-6) on how to get it inside the garage. The only problem is though, if you crash it even the slightest bit, it will explode (engine is on fire). The Jet will not explode if you do not hit walls too hard. Apparently if you do get glitch the jet in for the insurance, it might explode during the animation, if that is the case then you'd better hope you are lucky.
8. If you get it inside the garage again, you got it

And in case you are wondering, getting your jet back is free of charge from Mors.

IMAGES

[ Register or Signin to view external links. ]

Image 1 - How to position Jet (This position is closer to the edge then when I first did it, but it still works, so it can be there, or a little more to the left.
Image 2 - Another Angle
Image 3 - Where to press y after jet is in place (if your character moves when you press y, reposition yourself, for him to teleport after pressing y he must be standing still.

This also works for the Mallard.

[ Register or Signin to view external links. ]