Employees have a much greater incentive to save in KiwiSaver because it is compulsory for employers to contribute 3 per cent.
But around 5 per cent of New Zealand's workers are self-employed, 10 per cent work for more than one company and there is talk about a growing number of Kiwis doing different "gigs" for their work.
Hartmann said it had been wondering for some time how to get more self-employed people to contribute to KiwiSaver.
The extra cost to Government could be contained by limiting the incentive to the first 10 years of membership. That would cost the Government $20k - similar to paying the $521 over 40 years.
Hartmann he hoped that by 10 years a savings habit would be established. Putting the money in earlier would also make the most of compounding interest for the remainder of the member's term.
"Dialling up the Government contribution would add extra incentive for members to put in enough to gain the Government matcher each year."
The proposal is just one being considered by the interim Retirement Commissioner Peter Cordtz as part of the three-yearly review of retirement policy.
Cordtz said the idea was worthy of discussion.
"We're keen to find ways to make the KiwiSaver structure as fair and attractive as possible to all New Zealanders, whether they're in paid employment, self-employed or taking time out of the workforce," he said.
"This suggestion could encourage a wider range of people to save more towards their retirement."
Cordtz will consider the proposal along with public feedback and submissions before deciding on which recommendations to include in his report to Government in December.
Public submissions on the review are open until this Thursday, October 31, and can be made through the CFFC website.