Based on his height, I wouldn't buy the Flash Pass. There are a number of rides he can't ride like Superman, Raging Bull, V2, Batman the Ride, X-Flight, and considering he's just a little below 48, he probably can't ride American Eagle, or Viper.
What you can do though is this:
THRILL SWAP
Parents of children under 54" can notify a ride operator they'd like to participate in a Thrill Swap. This allows one parent to stay with the child while the other rides. Then they swap places! Ask any ride operator for more information.
This is so he can be with you at all times. To me, the most packed lines for the Flash Pass would be Superman, Raging Bull, X-Flight (but this you have to buy a higher priced Flash Pass which I don't think it's worth it. That line was shorter than Raging Bull last time I was at the park). Dark Knight is a longer line with the Flash Pass, but the last time I was at the park (again), the line was shorter that the regular people skipped the Flash Pass person all the time.
In general, I don't even see a reason for a person to get a Flash Pass this early on in the season especially during a weekday. A Friday or a Saturday, maybe... If you were talking July, August, October, than go ahead and buy one, but in EARLY June on a weekday, nah.
On top of that, crowds will also be in waterpark by that date. If you went this week or next week during weekdays, there is no waterpark open, so people should expect the park to be a little more crowded than June 5th for instance because the waterpark can be a draw, but it also helps keep people away from the regular park.
"I've been staring at the world, waiting. All the trouble and all the pain we're facing. Too much light to be livin' in the dark. Why waste time? We only got one life. Together we can be the CHANGE. So go and let your heart burn bright"