Allow multiple Issue Security levels to be selected

It would be valuable to allow more than one Issue Security Level. This would reduce the need for multiple levels to match the different combinations of Roles.

For example, my company would like to create a Infrastructure Upgrades project. This project will involve many outside consultants and internal staff. I can use roles for permissions, and I can create the following issue security levels based on the roles we have - a sampling could be
Omniware Internal
Sales
Network Admin
External Gui
External Web Services
External Developers

This allows me to create issues for Sales people only that NetworkAdmins can not view.

If I want to assign an issue that both the Sales and Network Admin roles can see (e.g. a task relating to a product install at a client site), I would then need to create another security level for Sales_and_Network.

So, if I have 5 levels representing 5 types of 'employees/security levels', I need to create 5 factorial (120!) levels to allow for all the different combinations.

Instead, I would prefer to simply select multiple security levels for an issue, i.e. "Allow the Sales and Network Admin levels to view this issue"