  We apply bulk holographic dark energy in general braneworld models with a
Gauss-Bonnet term in the bulk and an induced gravity term and a perfect fluid
on the brane. Without making any additional assumptions we extract the
Friedmann equation on the physical brane and we show that a
$\rho$-$\rho_\Lambda$ coupling arises naturally by the full 5D dynamics. The
low-energy (late-time) evolution reveals that the effective 4D holographic dark
energy behaves as ``quintom'', that is it crosses the phantom divide $w=-1$
during the evolution. In particular, the Gauss-Bonnet contribution decreases
the present value of $w_\Lambda$, while it increases the growing rate of
$w_\Lambda(z)$ with $z$, in comparison with the case where such a term is
absent.
