Capital markets were not nearly as fully developed as they are today when stocks were introduced into the world. Providing capital for new or existing enterprises would not be a problem.

A nation could simply declare stocks to be null and void. Buyers of pieces of paper have to be aware that they can become worthless for any number of reasons.

Another option would be to make buying/selling them illegal. Holders of stocks could redeem them (based on some historical value for each stock) in a form of quantitative easing: the money to redeem them (i.e., permanently liquidate them) would simply be created by the central bank. To prevent a rush to redemption, their value would be adjusted over time for inflation.