Support for static routing commands for PIX ("route <interface> <destination> <gw>") has been recently contributed by Steven Mestdagh <steven at openbsd.org> to the project. Thank you Steven!
This is done in the way similar to the routing support for Linux, you just add rules to the "Routing" rule set object. I then extended his code to add support for the "ip route " commands for IOS. In the case of IOS, there is no "Interface" column in the routing rules but you can put either an object representing gateway or router's interface object in the "gateway" column, in the latter case fwbuilder generates command "ip route <destination> <interface_name>".
Now Firewall Builder supports generation of static routing commands for three platforms: Linux, PIX and IOS. This is available in v3.0.4 build 732 and later, you can download packages from the nightly builds site at http://www.fwbuilder.org/nightly_builds/fwbuilder-3.0/
Please test, your feedback is very welcome.