C++ - Use enum from template class without template parameter

If you want to enclose your enum in a class definition for reasons (I cannot say what's the real problem), you can still introduce one more class that isn't a class template and contains the enum, then inherit from that with your class template. That's all.
As an example:

struct SomeBase {
    enum SomeEnum { SOME_FLAG };
};

template<typename>
struct SomeClass: SomeBase {
    // ...
};

Use this:

SomeBase::SomeEnum::SOME_FLAG;

Instead of this:

SomeClass::SomeEnum::SOME_FLAG;

Whenever you want to access the enum directly.
Something like the following remains valid anyway:

SomeClass<void>::SomeEnum foo = SomeClass<void>::SomeEnum::SOME_FLAG;