We are working on a further workaround which includes precompiled petsc4py, slepc4py, dolfin and mshr. Please join the #colab channel on the fenicsproject slack for further info, and report your feedback there. See Community – FEniCS Project for info on how to join slack.
For now I refrain from posting the workaround here because we might need to tweak it a little bit in the next few days, and it is more convenient to have the feedback, discussion and updates happening in one place (#colab channel on slack) rather than scattered in several different platforms.