Creative Uses of Google API

Connecting their Google accounts with the installation could potentially allow the users to check their emails and calendar.
The user will have to make gestures to interact with wall but it will be simple "point-and-click" type interaction.

He/she simply has to turn away from the wall to stop their interactions and continue to have their silhouettes displayed on the wall.

The silhouettes could also carry notification bubbles that could inform the employees if they have new emails or meetings coming up.
This could allow users who do not necessarily want to interact with the wall could quickly learn their agenda and encourage interactions.

However, it should be also noted that these could be private information that the users would not want to display it on a communal installation in a public space.  

Another way you can use Google API is to use Weather data to change the aesthetics of the backdrop of the installation or the color scheme of the silhouette.

Based on the temperature, the color could change from warm to cold or based on the weather, it could show sun, rain, snow and so on.