  A technique for the simulation of dark bremsstrahlung for electrons and muons
in GEANT4 is presented. The total cross section is calculated using the
Weizs\"{a}cker-Williams approximation and the outgoing kinematics are produced
by scaling events produced in MadGraph/MadEvent to lower incident lepton
energies, allowing the simulation to account for thick targets and lepton
sources without fixed energies. Compared with dedicated samples produced at an
arbitrary particle energy, typical precision of better than 5% is achieved.
