Monteith's character Finn Hudson will be written out of the show in the third episode which will "deal directly with the incidents involved in Cory's passing and the drug abuse in particular," Reilly said Thursday during a Television Critics Association panel in Los Angeles.
Reilly adds that producer Ryan Murphy will also shoot PSAs with cast members in character, "as friends of [Finn's]. They're going to speak directly to the audience and I think they're going to be very impactful."
Addressing Monteith's tragic death, Reilly said, "You see some people struggling with addiction and it's clear. Cory was a big, open, wonderful life force. He was not a problem. He didn't look like [a drug addict]. He looked straight as an arrow."
Continued Reilly: "He was very open about [drug addiction] in his past; not as open about it in the present ... Everybody was ultimately shocked because it was an accident that happened to somebody struggling with an addiction."
The proceeds from the episode's music sales will go towards a fund in Monteith's name, Reilly said.
Glee will resume production next week; the first episode will air Sept. 26.
Fans of Monteith may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.