Multiple Dynamic Participants in Workflow?

Is there a good way to assign a workflow step to multiple participants that aren't necessarily in a group together? One of our steps allows the workflow initiator to create a list of who the next participants should be, so i then need to use that list in the next step. But it seems to me that only single users or single groups can be made the step participant.

The only idea i have currently is to create a new sub-group during the workflow, assign those users to it, and delete it when the workflow completes.