Changing Split Tunnel VPN to Tunnel All Traffic

Consider the following network diagram: https://imgur.com/PCMu1cX

We are considering the removal of our .PAC files on our Branch Office computers and tunneling all Branch traffic through our Datacenter, rather than the current split-tunnel design. I think that tunneling all traffic over the VPN Connection between the two ASAs should be fairly simple. My dilemma is how do I then get that traffic destined for the internet and sourced from the Branch office to flow through the Cisco 3560-G at the datacenter so that it can be trasparently redirected through our Web Proxy for filtering purposes, since the datacenter ASA would normally just route this traffic straight out to the internet?