You can do several things. Amongst them:
1. Create a group policy and assign a VLAN that does not have DHCP and does not go anywhere. Their devices will be place on that VLAN and it will give them a failure as they will not obtain an IP.
2. Increase your DHCP pool, create a policy that has very limited Bandwidth (10s of Kbps) and assign it to mobile devices. This will make the WiFi for mobile phones so slow that they will prefer to use the LTE connection.
3. Stop using PSK and start using a radius server to authenticate. This will not allow their mobiles, which are not in the Radius server, to connect.
4. Similar to option 2. Increase your DHCP pool, set the SSID with very limited Bandwidth (10s of Kbps) and put a splash page telling them not to use WiFi. Assign to your corporate devices a whitelist policy. This will make any device that connects to WiFi go really slow and get a splash message about their non compliant behaviour. The corporate devices that you whitelist will not be BW limited nor get the splash page.
it is Friday. I encourage you to play with all of the Dashboard options and see how the users react!
Happy weekend.