In this case, I would use Dispatch. Create an Action that executes for this transition. Use the Conditional Jump and Labels in the script to create If/Then scenarios. If the logged in user is X then set Dept 1 to X. If the logged in user is Y then set Dep2 to Y. You should be able to pull it off with 1 Action. Unfortunately, you will need to specify the specific user as I don't see a way to apply this to a Group (probably becasue a User can be in more than one Group).
Yeah, I was disappointed about that as well. It is still better to setup a parallel transition the old-school way - different transition for each approval, from the same transition, then loop back with a condition or proceed with an opposite conditon.