Honestly, I can't fully understand why you would want to limit someone's innings that way unless you are trying to screw him out of his bonus. OMG. Is that it? Is that what you're trying to do DFyvie?!?! Someone call the players union immediately!!
No, seriously...I would probably set a pitch limit instead. If your goal is to go easy on his arm then the pitch count is a hell of a lot more important than a limit on innings. Since you manage Pitch-by-Pitch do what you've been doing and keep track of how many pitches he usually throws in 6 innings of work - or look at his stats and divide pitches thrown by games started for a quick & dirty average of pitches per appearance.
I don't know enough about Noah to recommend a conservative pitch count limit. On my team, I have Randy Johnson and I feel comfortable allowing him to throw 20-25 more pitches per appearance than my other four starters. He threw a lot of pitches in real life too. I also have Greg Maddux in my rotation. I've gotten complete games from Maddux with 90 pitches multiple times.
Limiting by innings can be dangerous if Noah doesn't have such a great game...walks...an error or two by the fielders... maybe he's not giving up a ton of runs, but if there are a lot of singles - all that adds up fast.
Good luck!