I'm not the authoritative source here, but it sounds to me like this
is out of ID's control. You touchscreen is nothing more than a
secondary mouse as far as the system is concerned. And ID switches ALL
input from the master to the slave with focus. This includes ALL the
master's keyboards, and ALL the master's mice (of which your
touchscreen is one).
To do this, you would have to have a way of making ID ignore input
from a specific device. I know of no such functionality.