A full installer is available for Beta 2.
The command has changed since Beta 1 for how to make a bootable USB installer (since the name of the installer has changed).
You can get the full installer of Beta 2 by reinstalling the macOS Developer Beta Access Utility which will open the System Updates Preferences pane from where you may download it.
You can then format an 8GB USB as HFS+ Journaled, call it Untitled and run this command in Terminal:
sudo /Applications/Install\ macOS\ Mojave\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
That will make the Bootable USB installer for Beta 2.
The command has changed since Beta 1 for how to make a bootable USB installer (since the name of the installer has changed).
You can get the full installer of Beta 2 by reinstalling the macOS Developer Beta Access Utility which will open the System Updates Preferences pane from where you may download it.
You can then format an 8GB USB as HFS+ Journaled, call it Untitled and run this command in Terminal:
sudo /Applications/Install\ macOS\ Mojave\ Beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled
That will make the Bootable USB installer for Beta 2.