  The use of a band offset between the two leads of an electron pump driven by
a local oscillating voltage is shown to increase the pump current dramatically.
The structure of the electron transmission suggests the existence of dominant
inelastic channels which we call pipelines. This permits the formulation of a
simple model that gives a physical account of the numerical results for a
realistic device. A spectral analysis reveals the pump current to be carried by
scattering states with initial energy deep within the Fermi sea and not at its
surface, thereby rendering the effect insensitive to temperature. We show this
is compatible with the current flowing near the Fermi surface in the leads.
