Adding Child-Business-Unit security roles to a solution

I'm having some trouble adding security roles to a solution so I can export/import from dev to test/prod environments. The process seems like it should be straight forward (Add Existing > Security > Security Role), but this only seems to work for roles within the root business unit, and any roles belonging to child business units result in the following error: "Subcomponent cannot be added to the solution because the root component Role is missing". I expect there is an option to adding Child-Business-Unit security roles to a solution beside Parent BU.