Exposing parameter types in a perfectly-forwarding function avoiding code repetition

I have an annoying scenario where I need to defer the initialization of some object state and allow the user to construct one on demand. E.g.

// user code

context c;
// ...do something...
c.initialize_state(a, b, c);

// library code

class context
{
private:
    class state
    {
        state(A a, B b, C c);

        state(const state&) = delete;
        state(state&&) = delete;
    };

    std::optional<state> _state;

public:
    template <typename... Xs>
    void initialize_state(Xs&&... xs) 
    {
        _state.emplace(std::forward<Xs>(xs)...);
    }
};

As you can see from the code above, the interface of context::initialize_state tells the user nothing about how to initialize context::_state. The user is forced to look at the implementation of initialize_state and then look at state::state to understand what should be passed to initialize_state.

I could change initialize_state to...

void initialize_state(A&& a, B&& b, C&& c) 
{
    _state.emplace(std::move(a), std::move(b), std::move(c));
}

...but this has a major drawback: there is code duplication with state::state, that needs to be manually maintained in case the argument types change.

Is there any way I can get the best of both worlds (DRY and user-friendly interface)? Note that state is not movable/copyable.