Tell people to upload a full site map to Google on the day of the launch or at least the option to specify how much pages the site contains (estimate).

Webmasters that go through the registration process are no black hats.

People would also not mind to provide business contact and emergency technical contact information if that is being used for good things that benefits them, such as providing advanced warning about major site changes, additions and launches.

Google can then in return also contact a webmaster, if they see problems. Some of it can be automated (e.g. notifications about crawl issues), others by a human (questions regarding the hardware capabilities of the new launched site for example).

You don’t want to kill the new site, but the owner also does not want that you nag just the homepage for several weeks without even to attempt a deep crawl).