  We present an implementation of the dual foliation generalized harmonic gauge
(DF-GHG) formulation within the pseudospectral code bamps. The formalism
promises to give greater freedom in the choice of coordinates that can be used
in numerical relativity. As a specific application we focus here on the
treatment of black holes in spherical symmetry. Existing approaches to black
hole excision in numerical relativity are susceptible to failure if the
boundary fails to remain outflow. We present a method, called DF-excision, to
avoid this failure. Our approach relies on carefully choosing coordinates in
which the coordinate lightspeeds are under strict control. These coordinates
are then combined with the DF-GHG formulation. After performing a set of
validation tests in a simple setting, we study the accretion of large pulses of
scalar field matter on to a spherical black hole. We compare the results of
DF-excision with a naive setup. DF-excision proves reliable even when the
previous approach fails.
