Im not 100% sure, but would the following work?

GRANT EXECUTE ON SCHEMA::SchemaName TO RoleName

Admittedly I am not sat on SQL right now so cant test and as said, I work in a much simpler environment where I use the GUI for permissions as we dont have that mnay objects in each schema.

EDIT: I dont know how many more get out clauses to put in if it doesnt work!!!!!!!