How to make a block sittable?

[Flurry]

I'm wondering how to make a block allow a user to sit on it, so like when the user presses a certain key on the block it'll make them sit down.

Does it have to involve with positing the character or anything?

[DavidM]

Create a custom entity at the position of the block when it is right clicked, and mount the player onto it. Note that the entity should destroy itself when the player gets off.