Absolutely. Plugzio is designed to be retrofitted.
This type of an outlet is fairly common in parking garages:
Here are the instructions on a possible way to install Plugzio on a single gang outlet.
Step 1: Remove the existing outlet from the box (make sure the breaker is OFF)
Step 2: Place it on top of the two gang box and mark the standard hole punches on the back of the 2-gang box.
Step 3: Drill the existing screw holes inside the two-gang box.
Step 4: Align the two-gang box with the existing hole on the single box and screw it in.
Step 5: Finish installing Plugzio