How can I setup 3 hosts files on our corporate iPhones?

we use iPhones for our company and also use forticlient vpn to access our intranet. Our forticlient setup must be in split tunnel so that our users dont consume bandwidth from our office network unless absolutely necessary. Our issue is that we have 3 internal websites that our iPhone remote users need but Fortinet is not supporting the vpn client from the App Store and the split tunnel is not using our internal DNS to resolve these 3 internal resources. Does anyone know how to setup 3 hosts files on our corporate iPhones to access these 3 resources on a split tunnel? I have opened a ticket with Fortinet but they are saying that I need to go full tunnel mode for our iPhones and that split tunnel is not supported.

[Re-Titled by Moderator]