A route to where?
What is the need for this?
Have you selected Routed VPN Traffic or Bridge VPN Traffic in your SSLVPN setup in your firewall config?
I use Routed VPN Traffic but I have a 4G LTE modem on my laptop.
And my provider doesn't give me a public IP address directly. I get a private IP as 10.x.x.x/8 and my subnets at home are 10.0.1.x/24 and 10.0.2.x/24...
So I have to add route manualy on my windows to force use my VPN gateway.
I would like to push these settings from the watchguard directly.
Since the VPN client does not get the same virtual IP addr upon each connection, a static route entry won't help.
I do not see a solution to your problem via the SSLVPN client.
If possible, change the subnet range being offered by your 4G LTE modem, such as shown here:https://kb.netgear.com/31160/How-do-I-change-my-4G-LTE-Modem-s-IP-address-range
I have a workarround by adding routes manual from a batch file when SSLVPN enabled.
I cannot change my 4G LTE subnet range because I use the internal 4G modem and the range seems to be provided by SIM card or something like that...
Thanks for you help !