How about an admin screen for automatically generating a large number of vouchers in bulk?
Admin screen would work like this:
Enter voucher code prefix.
Enter length of voucher code (prefix + random alphanumeric value).
Number of vouchers to be generated.
Other voucher options (default to use once only).
Button to export all the vouchers generated by above (including date used) as a CSV file.
A separate backend process would be used for printing vouchers from the CSV file. The printed vouchers could then the handed out / attached to other products at physical point of sale checkout.