Proxy for Cellular / Mobile

Background: Our enterprise has recently (01-Oct-2017) changed from open internet SIM's to APN SIM (M2M). When connecting to the APN, it forces the user to log onto our enterprise VPN. Everything works 100% for intranet, but cannot access the internet. The reason is that we have removed the proxy settings from the VPN (for security and business reasons). MS Windows computers do not have a problem, as you can set the proxy. Issue is with the iPads, as is there is no place to enter / configure the proxy. The VPN software we are using is either Cisco VPN or FortiNet Client. Question: Is there any where / how we can set the proxy on the iPad?