Safari proxy settings with VPN connection

Hi all,

I am using OS X 10.5.6 and Safari 3.2.1.
I connect to the internet using a 3G USB stick (ppp0). Then I create a VPN connection using F5's Firepass.
A new interface (ppp1) is created by that VPN process and a default route is added / replaced that now points to the new VPN interface ppp1. That interface does not show in any of the network configuration files or GUIs I know.
Safari however seems to see that interface. And since there are no proxy servers configured for that interface and proxy configuration is interface specific, Safari does not use any proxy server but tries to connect via the default route pointing to my VPN interface, which point to my company network and not the internet.
Now in my company network there is a proxy server I would like Safari to use. But since I cannot configure a proxy server for interface ppp1 it will just try to connect directly which obviously fails.

Does anybody have an Idea how I can make Safari using a proxy server?
(Modifying the routing table to use company network and internet simultaniously is not an option because the VPN process deletes any routes using it's interface but the default route)

Any help is greatly appreciated.

Cheers
Jan Ole Kastens

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