Unless you want to plug a keyboard into your usb port, you can code a state to put your character into that can pause the game. For example you can code that when you hit the start button it will send your character to a custom state & inside the state you can add stuff like this.
[State 0, AssertSpecial]
type = AssertSpecial
trigger1 = time >=0
flag = timerfreeze
[State 0, Pause]
type = Pause
trigger1 = time >=0
time = 1
ignorehitpause = 1
persistent = 1
to get out of the state use this
[State 0, ChangeState]
type = ChangeState
trigger1 = command = "s"
value = 0
ctrl = 1
;anim =
;ignorehitpause =
;persistent =