Ejector pins or tabs to pull it out would work fine. Of course, if you're not concerned about destroying the original mold, you could just force it out. My general plan (if I was working with machinable wax) would be to have two different processes, one for if I want a "one-off" part, and one for if I want to cast multiple parts. If it was one-off, I wouldn't be concerned about destroying the wax mold (because I wouldn't expect it to stand up to multiple uses anyway). If it was for casting multiple parts, I'd machine a positive in the wax, and use silicone to make the mold.