While there is no one-click solution, this is possible using copy/paste.
- Find the original element associated with your virtual class and in the navigator copy the styles for it (important note: currently relative styles are not copied with the other styles, so these will need to be copy/pasted into the global class separately)
- Create your new global class and paste the styles you copied in step one
At the very least this is faster than recreating the global class from scratch if it contains a lot of style rules.