You can try the alternate method listed here:
Personas show as "On Behalf Of"
One side effect I've found of using this method though- it gives the parent user two 'Calendar' named calendar entries which can cause issues with color coding if they are using one color for their 'Calendar' and another for the child 'Calendar' (new entries will show up with the color of child's 'Calendar' although they are attached to parent's 'Calendar').