You can deploy TOFFEE along with your existing VPN devices you can do the same as shown below. This will allow your VPN devices to encrypt your TOFFEE WAN Optimized network data. It will also reduce the load on these VPN devices (and VPN Network overheads) as the traffic within the VPN tunnel is WAN Optimized!
NOTE: Make sure about the VPN deployment topology done in the right order. Else TOFFEE (LAN side) may get VPN encrypted packets which may not be possible (and or difficult) to further optimize. Hence always make sure to deploy them in a topology suggested below so that TOFFEE devices are out of VPN tunnel.
Learn more about: TOFFEE WAN Optimization deployment