The next releases of 3.7 and 3.8 will include _Py_SetProgramFullPath() functions for embedders to set the eventual value of sys.executable before calling Py_Initialize(). It's undocumented and not guaranteed stable (and indeed, it looks like Victor is already working on another patch that may see it removed before it's ever released), but it's in now as a workaround for the cases that need it.