So you're already on the hook for the $658 regardless. It's the extra $292 that's at issue here and, moreover (I trust), whether the child needs it. That extra $3,504/year isn't chump change, but if you believed in the programs you would find a way to make it work at your income.
This sounds to me to be not about money for you as much as whether the kids is benefitting, or even suffering.
If you feel that the kid is being overloaded, then bring that argument and be prepared to back it up e.g. kid is tired, grades are suffering, no down time, etc.
So all you have to do is not agree that they be given the extras and you are not liable? I think not.
And interesting arguement being suggested in a case of a friend is the heavy involvement in out side activities is having a detrimental effect on the schooling of the children of a friend. His arguement that he will be going to court on is the children should be home more either in his house or the mothers doing what will be most important to the best interest of the child in insuring a good education to prepare for life long skills...as opposed to playing games 5 nights a week and not succeeding or doing well in classes as they are not prepared for classes due to the outside activities.
There is already recognition in some case law that hockey is often frivolous and rarely going to result in any concrete future....
In my view, that argument definitely has merit. Putting kids in activities all the time is too busy. I think the whole "soccer mom" stereotype woke us all up to that a decade or so ago. And when there are two homes involved, that adds to the "busy mix".
Kids need down time too, or free time without structure where they can chill out. There's even an argument that constant structure doesn't teach kids to be responsible for their own stimulation.
Even sole custodial parents are required to "consult" with the other parent, but if there is disagreement and the other parent takes it to court, the custodial parent's views will be given greater weight.
So no, it isn't just a case where all you have to do is say no and the section 7 expenses are off the table.
On the other hand it's not a slam dunk for the custodial parent either. At the end of the day, the activities have to be in the kid's best interest.