Hi Damien,
Yes, you can leverage PBR here.
1. Create an extended ACL, with destination IP == the IP of the website
2. Create a match group and add the ACL to this
3. Create an action group, pointing to ethernet3 and the gateway IP as next hop
4. Create a PBR policy and add the Action group and match group to it
5. Bind the PBR to ethernet1 interface
I am assuming you would already have a default route through ADSL as well, to serve as the backup internet link. If not, add it with a higher preference value than the VDSL route.