This works (I just tested it):
Types a 2 on single click and a @ on press-and-hold (the two @ around the character on the tooltip indicate it's a press-and-hold command).
Having said that, I think it's A LOT faster to press another key to switch the "mode" of the keys (i.e. SHIFT/CAPSLOCK), than press-and-hold the key to get the desired function. Furthermore, press-and-hold may be a lot harder on some touch-screens than you think -- specially while the car is MOVING.
In that sense, you could use:
And the key will type 2 on standard presses and will type @ when you press shift BEFORE you press it, or when caps lock is set (Those are the SHIFT and CAPSLOCK OSK commands -- not on an actual keyboard). They will all be standard press of the buttons, no press-and-hold necessary.