Nonlinear laser processing of dielectrics with ultrafast lasers has been extensively studied over the last years and successfully applied to the production of photonics and micro-fluidic devices. Still, problems related to the presence of strong optical nonlinearities make it difficult to optimize the spatial intensity distribution in the focal region (SIDFR) in some cases. Methods providing a rapid estimate of the latter, even approximately, can be of great help for optimizing processing strategies and in other applications conditioned by nonlinear propagation like spatial soliton shaping. We have developed a numerical method for estimating the SIDFR inside a dielectric material, considering nonlinear absorption, nonlinear refraction and spherical aberration for laser beams with arbitrarily shaped wavefront. It is based on a generalized adaptive fast-Fourier evolver and has been successfully tested for flat wavefronts in subsurface processing. In this work we demonstrate its applicability to complex wavefronts, like those that can be generated with spatial light modulators (SLM). For this purpose the beam wavefront is described using Zernike polynomials before being propagated inside the material for different depths, pulse parameters. The results obtained show that under certain conditions, nonlinearities can be not only controlled and pre-compensated but also exploited for producing tailored SIDFRs.