The new version of the software (not yet released) does include groups in memo sets.
In the meantime, you could just add a column called Group and get mostly the same result.
In some cases, it will make sense to use additional columns instead of groups when converting a system to a memo set. For example, if you have a PAO system with one group for Person, another for Action, and another for Object, it would make sense to have columns for those in a memo set so you could see everything together.