If he only has 9mg of Suboxone and is using it to detox from a normal full agonist opioid, then he shouldn't be in too much discomfort. He won't have any withdrawals from the Suboxone because it simply isn't enough to create dependency. It won't be as comfortable as if he was able to take 4-8mg per day for seven days, but 2mg/day is way better than nothing. I'd probably take 3mg on day 1 and then 2mg a day for four more days.
Regardless of how he uses the Suboxone, given how little he has, it's not going to make a HUGE difference (as in night and day) in how much discomfort he's in during his detox. That said, he's best off taking the smallest dose possible (probably 2mg in his case) for at least four days (ideally it would be for seven days, as this is normally how long the entire acute withdrawal process takes).