"We loved Cory and we loved Finn and it feels like a huge loss and a huge heartache not to have either of them around. We're trying to craft an episode that's not just about us grieving but about a lot of the young fans grieving," he explained.
But writing the scenes has been delicate work.
Murphy initially thought about imitating the story of Monteith's death onscreen but he's now assuring fans Finn will not OD.
"We have decided that we're not going to have him pass from that," he said.
Instead Murphy's team will leave the ending open to interpretation, which he hopes will make remembering Monteith a celebration.
"Basically, what we're doing in the episode is we are not telling you yet, or maybe not at all, how that character died," he said.
"The idea being, how somebody died is interesting and maybe morbid, but we say very early on in the episode, 'This episode is about a celebration of that character's life'.
"That might be weird for some people, but it felt really exploitative to do it any other way," Murphy continued.
The screenwriter said the cast and crew, including Monteith's former girlfriend Lea Michele, have been leaning on each other throughout this difficult time and plan to take time off after the memorial episode is finished.
"There's been tears on set. It's been hard for a lot of people. But the really difficult thing is coming," he said.
"We're just now finishing it, and at the end of the week we'll send it to [the studio 20th Century Fox Television] to get their approvals.
"After that, we're going to take two weeks or three weeks down to get our heads together because it's been a really hard thing to write."
The Glee memorial episode will begin shooting this week.
