To answer my own question (for the people who read it later), I added a little script to the buttons to check manually (I have emulate mouse from touch enabled).
var pressdown_position = Vector2()
var press_threshold = 20
if event is InputEventMouseButton and not disabled: #with InputEventTouch it didn't want to work well
pressdown_position = event.position
elif event.position.distance_to(pressdown_position) <= press_threshold:
_on_button_pressed() #call the function you want the buttonpress to call