According to that thread, after changing the supervisor access in the system parameters, a supervisor can log into the CCX appadmin and reskill the agents. I tried it out on my CCX 11.6 system and it worked. So, I may be wrong about the APIs not working for a supervisor. I think after changing the system parameters, the supervisor can use those APIs I listed above. Then, you can use those APIs to build a custom gadget to do what the customer requested.