Inland Revenue has produced operating statement 19/01. It sets out the criteria for a person to be granted an exemption from the requirement to file various returns or information, electronically.
The gist of 19/01 is that if it is unreasonable to expect a taxpayer to file electronically, an exemption will be available. The paper lists reasons electronic filing could be a hardship.
Special software is not required. Completing the appropriate form on the IRD website qualifies for filing electronically.