Thats why I said only try that if talking to him doesn't work. Obviously this is the best solution, but sometimes its going to take more. And you don't say "u can't force me" you just start slacking off in practice (not necessarily obviously so). It might take awhile but eventually the kids dad will get tired of nagging.
I'm sure if I was still somewhat competitive my parents would still be forcing me to run five days a week.