Homestead now supports HHVM out of the box! To use it all you need to do is run the following:
vagrant box update
Next update your Homestead repo and in your Homestead.yaml file add hhvm: true:
sites: - map: homestead.app to: /home/vagrant/Code/Laravel/public hhvm: true
This is a nice upgrade and will at the very least make testing and playing with HHVM super easy.