Updated for 7.0
Click on the Settings icon (the gear) located to the right of the search bar. This will take you here:
In the horizontal navigation bar, select Events. A drop down will appear. Select Event Defaults. This will take you here:
Within the setting box, use the On/Off toggle to the left of Assign Non Member Orders To Groups.
If this is not on, your system will now allow you to assign Non Members/Guests to a Lieutenant/Group
Once this is on, you will add Non Members/Guests to a Lieutenant/Group as normal.
Follow the directions here to do this.