Almost assuredly no, for a variety of reasons including:
- Unless there was an enforceable agreement that the money would be used for a particular purpose, it will probably be concluded that the overpayment was a gift. Even if the ex-wife 'agreed' to use the money for that purpose, it doesn't mean that it is enforceable. And even if it is enforceable, it would need to consider the method and circumstances of repayment. And if you pass that hurdle, it it unlikely that repayment will be allowed to be offset against the ongoing child support liability.
- The money paid has no doubt been spent. The purpose of child support is to cover the expenses of raising the child. Those expenses are obviously ongoing and current (food, shelter, clothing, schooling and so on...). A court will be unlikely to enforce a situation which jeopardises payment for those current, ongoing expenses. For the same reason, it is discouraged that child support is pre-paid in a lump sum. The system is designed with the aim that the payment is made so that funds are available consistently over time.
Child support payments should be considered like paying tax. You have to pay it. You have no say in how it is spent, and you can only hope that it's used for something worthwhile. If it isn't, there's not a lot you can do about it anyway.