DrayTek Vigor2132F WAN without bridge

[mtk]

Hello,
I'm trying to install my pfSense box and I connected the WAN port to my DrayTek Vigor2132F modem and the LAN to the existing switch.
The problem is that the DrayTek Vigor2132F doesn't have bridge mode.

What would be the best way to set it up so the Internet Connection traffic would pass through the pfSense and be shared within the existing network?