Firstly, I just want to say that you are awesome! We deal with a BM who is the opposite of you, she does all she can to stop my SO from being a part of things like this, he has had to put it specifically in the CO stating that events that fall on his time are HIS!
He loves getting SD ready (well, watching me get her ready, but he helps pick the outfit lol), he loves dropping her off and picking her up, her excitement makes him happy.
Maybe offer to do all pick up/drop offs and buy present, offer him make up time (exchange pick up few hours earlier etc).
At the end of the day, you can't make the ex do certain things during his time, which seriously seriously sucks! But I guess (if you keep all communications) if he ever tries to go for more custody (never know) you'd be able to show the court how he is not very supportive of your DS's social development etc