He had numerous conversations with former Australian Prime Minister Tony Abbott, who was rolled by Mr Turnbull last month, and sensed an opportunity to lower the threshold for deportation for New Zealanders.
"When politicians on both sides of the Tasman talk about the fact that Australia and New Zealand are family, I think they actually mean that," Mr Key said.
"But one of the ways of demonstrating that would be a bit more flexibility about where the threshold is set for this particular policy."
Asked if he would characterise the detentions as a strain on the relationship with Australia, he said he would not, as the policy was not specific to New Zealand.
Mr Turnbull was a "reasonably sensitive guy", Mr Key said, but there were domestic political issues to any possible change to immigration laws.
"They are the challenges for us...but Australians are fair minded people and they certainly know there is that relationship with New Zealand."
Mr Turnbull and his wife Lucy will join Mr Key and Bronagh for a private dinner on Friday evening, ahead of a bilateral meeting between the two prime ministers on Saturday.
Last month Justice Minister Amy Adams announced the signing of a new information-sharing agreement with Australia, which would provide more details on criminals being sent to New Zealand, including a summary of offences, case history, fingerprints and photographs.
At the time, Ms Adams said the next step was to change the law to ensure offenders who arrive here were subject to the same oversight as they would have been if they served their prison sentence in New Zealand.
The Herald has documented the cases of some New Zealanders detained in Australia, including one man who was held in a police cell, where lights were left on around the clock, for nearly three weeks before being shifted to a detention centre.
Peter Dunne, leader of United Future, the Government's coalition party, last month said the response to Australia was part of a wider foreign policy that lacked any commitment to human rights.
He pointed to the "appallingly tardy" response to the Syrian refugee crisis and the case of New Zealander Philip Blackwood, who was jailed in Myanmar in December for insulting Buddha, as examples of New Zealand being hesitant to become involved until public opinion demanded it.
Mr Blackwood's father has also said he feels there is little political will to help his son.
This afternoon, Mr Key said he was limited in what he could say about what the Government was doing to try and help Mr Blackwood.
"We do lots of things behind the scenes and quietly where we can, and we understand absolutely the issue. But we can't make the situation worse for the person."
