Do you mean limiting a number of products or limiting a particular product. This topic may help you out? dbdave came up with a solution which is for one product only
Yes, and the .php version is still active on my test site. If you need it for more than one product, I can see if I can update the code, if it's only a few products. If it's quite a few products, it would get more complicated and need some more intensive coding.