I’m so happy that one of my scratch org pet peeves finally made it into the product for the Spring 19 release. It has not been possible to enable the Individual Object when creating new scratch orgs and IMO this has been lacking and a cause for many issues, discussions and workarounds in customer projects. But all this is a thing of the past now! Starting Spring 19 you may add the below orgPreferenceSetting to your scratch org definition file:
Now the setting hasn’t made it into the documentation as of this writing but I know that it’s in the works. No go and create scratch orgs with the Individual Object enabled!