I was thinking about this episode the other day and was always wondered if a better resolution could have been made.
I have always been unhappy that only the Doctor supported Tuvix's right to live and Tuvix seemed to be abandoned by the rest of the crew. I would have preferred if several more crewmembers would have backed Tuvix so it would not have been such a one-sided issue.
In Star Trek TNG there was an episode called 'Second Chances' which introduced Thomas Riker.
Due to a transporter accident, early in William Riker's Starfleet career a duplicate of him was left on a planet.
I think this happened before Voyager was transported to the Delta Quadrant.
So my idea is that several crew members are trying to find a way to save Tuvix's life and B'Elanna Torres brings up starfleet database records and finds the acticle about Thomas Riker and the transporter accident.
B'Elanna believes Captain Janeway would not approve of using this to produce duplicate Tuvix's so she keeps it a secret from her.
Tuvix is sent back to the planets surface as part of an away mission to collect food & supplies. Tuvix is last to be transported back and B'Elanna duplicates the transporter accident which leaves one copy of Tuvix to survive on the planet and the other arrives back on Voyager to be later split back into Tuvok & Neelix.