How do I configure Shrewsoft's VPN client to only route traffic to a certain IP address through the VPN?

Solution 1:

In properties window of VPN connection profile, go to (1) Policy tab. There you can add routes.

(2) Uncheck Obtain Topology Automatically or Tunnel All
(3) Click Add.
(4) Set Type to Include.
(5) Set Address to the exact IP you want. (6) Set Netmask to 255.255.255.255.

See also: Shrew Soft VPN Client Admin Guide: Policy Settings (Archived here.)

Solution 2:

To Compliment Nikola's answer further:

You would need to Disable the 'Obtain Topology Automatically or Tunnel All' check box first to reveal the lower part where you add the routes as per his response.

See: Similar Question (StackOverflow) for more details

Hope this helps