I usually run several applications that are of the same type, but have different icons that I want to group under the same preview/group.
Unfortunately, windows7 does not support this.
I think it would be easiest to modify the existing object code/hooks and allow drag and drop merging, but some kind of right click option addition or static config file that defines a group and specifies an icon would also work quite well.
What are your thoughts on the idea?