Assign workflow steps to groups/roles

Does anyone use roles/groups in his workflows? How did you implement them?
The example workflow assigns workflow steps to owner "null" and then uses
permissions
to see if a uses is allowed to see/change this workflow.
The problem with this implementation is, that it doesn't perform very well,
because you might need to loop over hundereds of steps assigned to "null".
How about adding a owner group field to Step? But now, if someone is in a
bunch
of groups you have to do a lot of queries.
Any ideas?

Philipp



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