Menzel will play the director of Vocal Adrenaline, the rival show choir that will provide New Directions' major competition in the upcoming regional competitions. Chenoweth will make a return appearance as former glee club all-star April Rhodes, but no, the formerWicked co-stars will not be sharing the screen.

"It didn't work for the storytelling, so it really wasn't necessary," Falchuk told reporters. "It's always story first … and then we kind of go from there … When you have people like Idina and Kristin who are such mega-talent stars, you have to get them just the right thing and you really want to treat them right."

Falchuk described Menzel as "incredible, and the episode with Kristin in it, I think, may be our best one yet. It's called 'Home.' It's the third one back, and it's so moving and hilarious and she is, obviously, Kristin, so you kind of can't keep your eyes off her."

Both producers were clearly thrilled to have worked with Harris as well. Harris will appear in a May episode as Bryan Adam, an anti-arts-funding board member at McKinley High who's a former rival of glee club director Will Schuester (Tony nominee Matt Morrison).

Falchuk said, "He was delightful, he was easy, he was all the things you wanted him to be. … When we were writing the character, we were like, 'Oh my God, what if for some reason, Neil ... can't do it? No one else can play this character; we'll have to rewrite the whole episode!'"

Brennan added, "I'm really excited to see the cut of that episode, because I think it's gonna be really, really good and really funny."

Menzel's role will recur throughout the nine episodes. When asked whether Chenoweth and Harris will return for future episodes, Falchuk demurred slightly while reminding everyone of the strong base of regular talent the show already has: "[When] you have talents like that, it's very hard to not want them back. The one advantage we have, I think, is that we have so many incredibly talented people in our … cast that … we don't need [guest actors] as much. But there are certain very special people that, of course, you'd always be interested in. But you know, you never know, is what I say."

The final nine episodes of "Glee"'s first season will start airing April 13 at 9:28 ET, after "American Idol" on FOX-TV.

—Thomas Peter