I'm not sure if this is what you're looking for, but you could use something called Alternate groups. First create two groups of Nurses instead of one. (Have the higher qualified nurse(s) be in a different group.) Then in your toolbox select the green '+' and select Alternate Groups to create a new Alternate Group. Add both groups of nurses to the Alternate Group list.
Now in your patient track, when selecting a Staff requirement, you can select the Alternate Group for any task that can be accomplished by any nurse. OR if the task specifically requires the higher qualified Nurse(s) you can select that group specifically.
Does that sound like what you're looking for?