You can add the platform behavior, and then set the controls to NOT default. This way the only movements the player can do are the ones you make in your events.
Now you can do this, add an instance variable to the player called "direction"
When the player presses right set "direction" to 1, and when he presses left set "direction" to -1
Player.direction = 1
: Simulate move right
Trigger once
: Simulate jump[/code:3ai6stug]
[code:3ai6stug]Player.direction = -1
: Simulate move left
Trigger once
: Simulate jump[/code:3ai6stug]
[code:3ai6stug]Player hits ground (a platform behavior condition)
: Set Player.direction to 0[/code:3ai6stug]
Then you can play around with the max speed, acceleration, gravity, etc to get the movement the way you want