The method you are using is one way to do it. And it's probably the best way - even though it involves more work. What this method does is give you complete control over every seat of the group. You also control how the money shows up in the reports.
The other way would involve taking a block of seats off sale - by modifying the available price codes in the seating plan. Then, members of a group would purchase seats in the "group section."
Both these methods are the same in that they both take a block of seats off sale. The first method though is a 2 step process to re-sell the seats. It's more work, but it does give better control. YOu don't have to worry about different groups being mixed up.