I don't follow you on the advantage or reason for only using the closed-over variable in one place, that being a function that returns it.
By "static method" you mean a sub that doesn't refer to any instance data (and would see the class name as the first parameter)? Is there a special technique for declaring those in a parameterized role or elsewhere? I did notice that using MooseX::Method::Signatures it doesn't like that as the first argument is checked against Object. But a regular Perl sub inside a code block (such as the role block) doesn't work right, so you must have some other way to declare that, right?