Currenty, the option for "Visibility" in a CMS block allows using Rulebuilder rules to pick if a block should be displayed or not.
Using this on a Product detail page is relatively useless, though, because there are no rules referring to the product being displayed. (There are rules regarding to products-in-carts, but those don't work here).

So, request: Add an option to the rulebuilder that checks the currently-displayed-product that can be used on the CMS templates. Might be extended to "current category being displayed" for more flexibility, too.