SSL VPN dynamic SNAT

Team,

with a UTM 9, i am connecting from my private network through a DSL router, that manages the internet connection to a corporate network via SSL vpn. 

The corporate network dynamically assigns a private address to my tun1 interface. 

To access the corporate network then, i have configured a SNAT rule, changing the source to the TUN0 address.

That works, until the vpn connection gets re-established and assigns a different tun1 address.

I am wonderung, how i can manage this, is there a way to use the tun1 in the SNAT configuration?

Any other/better way?

Thanks!