The series, which starred Kristen Bell as a student who moonlights as a private investigator, ran from 2004 until 2007.
Speaking to Entertainment Weekly, Thomas said that he had almost finished writing the project, saying: "It's close. A few key details left to solve.
"I'm preparing the pitch now - literally now. I hope to go in and talk to [executive producer] Joel Silver and [Warner Bros.] in the next week or two to see if they're interested."
However, he stressed that this did not mean that the movie was a done deal. "I'm going to give it my best shot and let the chips fall where they may...It's entirely possible I won't have an answer at the end of the pitch.
"They will want to consider [the pitch], look at some numbers - whatever it is people on the business side do - and then they'll give me some sort of response. Then, if they want to move forward, there's the deal-making that'll need to go on."