Unless you fire it at a speed if M5+ it will still end up going in the same direction as you. Any engagement of a hypersonic platform will, presumably be from the from quarter (otherwise it’s a hell of a tail chase), so counter measures need to be in front, not back.
Forget internal, presumably it would be carried externally as a stck and peel off using a solid state SCRAMjet capable of M10+. (X-43 type design but using a hypersonic launch platform rather than a rocket).