If we're really concerned about this - get rid of the network connectivity.
Obviously this is over simplified, but just make a simple locally ran app or web application that refreshes once a vote has been cast. Store the vote in a simple SQLite database and at the end of the day, have a voting official go to the machine, and unlock the case, press a button on the back, which prints out or shows vote counts on the back on a small screen or something. They then can report that to whatever commission, committee, or otherwise is monitoring the election.
It's all locally stored, maintained, and under lock and key.
Why does this seem so difficult? We don't need democracy hindered by "network connectivity", just make it more environmentally friendly so however millions of people times the size of the paper ballot isn't wasted needlessly.