There are no such options inside the web interface, but you can do it by using a template-custom:
mkdir -p /etc/e-smith/templates-custom/etc/openvpn/host-to-net.conf/
Then create a file named
/etc/e-smith/templates-custom/etc/openvpn/host-to-net.conf/90custom with your preferred editor and put your options inside it.
To apply the configuration, change something from the web interface or execute: