  We derive a vertex operator based expression for the kinematic numerators of
Yang-Mills amplitudes by applying the momentum kernel formalism to open string
amplitudes. The expression involves an $\alpha'$-weighted commutator induced by
the monodromy relations between the colour ordered Yang-Mills amplitudes, which
mirrors the $\alpha'$ deformed colour structure observed in open string and
semi-abelian $Z$-theory. The kinematic algebra given by this construction
contains the Lie algebra of diffeomorphism as an obvious sub-algebra.
