I can only say that I don't know a lot about proxy marriages. The country where I do know proxy marriages happen quite a lot is Israel, where couples actually get married by proxy marriage quite frequently because the laws there are limited to religious marriage. I don't know if there has been a particular problem in Israel with proxy marriage, but this leads to my suggestion, which is that you might want to study the experiences of other countries where this is permitted to see if there is any correlation and then to figure out, if there is, what might be the best policy response.
It's not my understanding—but I have not studied it—that this is a particularly serious problem with regard to the incidence of forced marriage, but having said that, I confess that I have not done a close study of it.