"In the end, the really simple message is of course of all these bars could apply [for special licences], but it's quite expensive and it's bureaucratic for them," he said.
"For a one-off thing like this, rather than put everyone through this process I think it's simpler to try and find a way through it."
National will consider narrowing the legislation's scope so the policy only applied to All Black games and knockout rounds.
The Prime Minister also said Greens' opposition was "par for the course" and the party was "always opposed to anything that vaguely good fun".
The Green Party's health spokesman Kevin Hague said Act Party's legislation was a "cheap publicity stunt" and Mr Seymour was "hijacking Parliament's time ... for a cheap gimmick".
"This is his ham-fisted attempt to be a man of the people but it actually has the potential to cause some real harm to communities up and down the country," Mr Hague said.
Mr Hague said that if the bill passed, "boozed-up" rugby fans would be spilling out of bars as parents were dropping their children to school.
He said pubs were already able to apply for special licences to open outside the maximum default hours, and many had already taken this option.
If Government introduced its own bill, Mr Hague said Greens would "give due consideration to it".
He said this option was preferable because it would not delay private member's bills which were due to come before Parliament.
Mr Seymour said shutting New Zealanders at home for the tournament "seems like a mean-spirited affront to community freedoms".
"The Greens do themselves no favours by locking themselves in as the party opposed to fun.
"World Cup audiences' only hope now is for this Bill to be adopted as a Government bill."
