[support] Select user with permissions for each node, but where roles or group is not usable

Hi, I have read the other thread, but my problem is different.

I have my content type "AB" with some informations (say a "download file possibility") that will be avaible only to the users that have buy the access to this informations. My the idea is to call a e-commerce, ask if the user have buy the access and if "yes" permit to the user to access to the informations.

I have thinked this way: in a hook_nodeapi() where $op = "view" verify that the user can access to that content (via ecommerce): if yes I change the $node->body with other info reserved for who buy the content, otherwise I change the $node->body with an info about how to buy the content.

Is this the correct way ? Are there better solutions ?

M.