Two user roles for one user?

Hi,

is it somehow possible to assign TWO user roles to one single user account?

(by means of a hack, or a plugin)?

I now there are capabilities which are more flexible, but I need to realize this using roles (because of a plugin that restricts content based on role membership).

The underlying problem is that I need hierarchical user groups (if I share a resource to the role “Subscriber”, then any member of “Administrator” should have access to it too…

Any suggestions how to proceed?