Obvious Way To Add To Group?

[Mike Kerner]

I have a group that I'm using for a background in a stack.  I want to add a
new object to that group without losing the data in all the fields in the
rest of the group.  Selecting the group and the object and asking to group
them will cause the old group to be destroyed and a new one to be created,
removing the data.

So how do I add an object to the existing group?