You probably don't even need to do that much re-engineering. The 'suffering' of uploads in a Malthusian existence isn't physical pain, just endless mental drudge work. They could probably just interfere with their emotional experience of time so that they didn't get bored or overwhelmed. See, e.g. Diane Van Deren who became one of the world's top ultra-runners (100-300 mile races) after epilepsy surgery damaged her perception of time.