Yes you can!
Tandem support (the ability to turn the Dec axis 90 degrees and mount multiple optical tubes side-by-side) is now available for firmware versions GEM 4.15 and higher for Celestron’s German equatorial mounts.
It is under SCOPE SETUP > OTA ORIENTATION. You choose the tandem settings before aligning your scope.
There are three options.
Normal is regular use of the scope without any tandem bar-scopes on the mount.
East is used when your scopes are facing east when the declination index marks are aligned.
West is used when your scopes are facing west when the declination index marks are aligned.