Rail movement that doesn't look like a game and watch

Hello guys!

I saw couples of topics on player's movement on specific rail. Like a Guitar Hero type of game for example.

My problem is that I'm able to have the sprite of the player move on the rails so the game is playable and works.

But I wasn't able to have a smooth transition like in the attachment, more something like a game&watch. As I'm designing that game for touch screen devices, I would like to be fluid and that a tap on the top or the bottom of the sprite would start the movement. I made a little schema to explain myself.

Thanks for the help!

[attachment=0:3ns8gzcw][/attachment:3ns8gzcw]

A capx would help.

Anyway... I think you could use easing or just simulate movement up or down with a stopper on the rails...