Custom Role Provider use Enum for Roles instead of string[] Hierachical order?

 Hi all,
I use windows authentication in combination with a custom role provider. The Roles are stored in a mssql database but i want to use my own schema that's why i am using a custom provider. Looks quite simpel as in this tutorial http://davidhayden.com/blog/dave/archive/2007/10/17/CreateCustomRoleProviderASPNETRolePermissionsSecurity.aspx.
But i don't want to represent the roles as string but as an enumeration. But the result value of GetRolesForUser seems to be determined as string
So what is the best approach for that?

So instead of:
 
public class SimpleRoleProvider : RoleProvider

{

public override string[] GetRolesForUser(string username)

{

List<string> roles = new List<string& ...