Aberrations of electron-optical components fundamentally limit the resolution of modern electron microscopes. Recent work has shown that the wavefront of a free electron beam can be modulated through the ponderomotive interaction with a shaped laser field, opening a route to aberration correction that avoids the geometric constraints of electrostatic and magnetostatic elements. Fully harnessing the flexibility of the ponderomotive approach requires the ability to generate laser intensity profiles on demand. We develop a phase-retrieval algorithm and an experimental setup based on a phase-only spatial light modulator that together provide this capability. The algorithm is tailored to the regime relevant for our application. An additional refinement step based on live camera feedback compensates for imperfections of the optical system. As a guiding application, we summarize the theory of the electron--laser interaction, identify intensity profiles suitable for correcting individual electron-beam aberrations, and experimentally generate these profiles with the developed setup.