How old are the DC? You can give them crappy PAYG mobiles that they never even take out of house. Then he can call them direct on their phones and you don't even have to speak to him. If he calls housephone get them to answer. Don't answer yourself. He will soon get bored.
This will get easier as the DC get older I promise you, as they will make their own arrangements with him and you will barely be involved anyway. They will be telling him they aren't seeing him as they are going to X,Yor Z instead.
When he calls to get DC have them ready ( tell them he is coming 15 mins earlier than expected) to go and let them open door and just go if they are old enough. When they come back just open door and then wander off.
My XH used to do this whole pitiful drama thing when he dropped DC off where he would make it sound like DS didn't want to come home and he would be saying things like "It's OK son, I will ring you later, I will see you on Friday, don't worry, it will all be OK" then as soon as the door was shut, DS was fine, grinning and happy. XH just wanted to make it all a huge drama.
I don't call the DC all the time when they are with him either. They often see it as an annoyance when XH calls them here and I just don't feel the need. Maybe every couple of days.
It will get better, it just takes time to adjust.