PBU and PPU allow you to give guests a button with a custom email domain. So if your client was LA Photo Party, then you could make a would be a button that says "@laphotoparty.com" which everyone at the party could use to save time and effort during email sharing.
Custom email domain can be added in Kiosk in Preferences, by pressing the "Set Custom Keyboard Email" button to access the option.
In PBU, it's in Settings under the MISC tab.