This sounds like a crazy cheat code from the Nintendo NES days haha... Up, down, up, down, left, right, A, B, A, B.My local shop installs remote car starters in manuals all the time. I have one installed in my car. I have to put the car in neutral and then pull the e-brake up 2 times. Then take the key out of the ignition, the engine will stay running until you get out of the car and shut the driver's side door.
If you have passengers in your car, make sure they don't open their doors until you performed the open mentioned steps and the key is out of the ignition. Otherwise, you will have to wait for them to get out and close their doors before you can do it.
I paid $500 to have this installed. But it's great in the winter if you leave the heat cranked and pointed at the windshield.