I'm not sure how large the paper needs to be to be recognized. Maybe you could have snippets that hold only a single identifier or syntax element and programs would be arranged by puzzling them together. That should be an appropriate granularity for manually placing (no fidgeting with tiny individual letters) while still allowing full programmability with minimal trips to the printer (only to create some new identifier).
I wonder if you could create a set of symbols which were sufficiently distinctive enough that you could hand-draw them and stand a chance of the computer recognising them. Difficulty level increasing again...
