There is no direct access to the routing tables.

With some (one) of the built in VPN types you get an option to only route traffic destined for the remote LAN. The option is on the L2TP VPN type, called "Send All Traffic".

I've not used the two other builtin VPN types, but I'd always assumed that with those you could control the behaviour from the server end, like you can do with an OpenVPN setup.

I use OpenVPN endpoints and the OpenVPN iOS app for my VPN needs.