Using tools to create a new namespace

I have a large codebase filled with names such as MyCompanyMyDeptMyType. This is making the code rather hard to read. I would like to use a tool to move all these names to a nested namespace MyCompany::MyDept.

My header files would look like

namespace MyCompany {
namespace MyDept {   
  // here goes the code with shorter names
}
}

and my cpp files would end up with using namespace MyCompany::MyDept; at the top.

Does such a tool exist? (clang-rename?) If not, is my best shot to write my own clang AST visitor?