You need a tap bridge, but that only works properly on 2.1.x. IIRC there are howtos here on the forum … somewhere, I wrote one of them somewhere.
You can do it on 2.0.x with the tap bridge fix package that fixes a few things in 2.0.x for tap VPNs that didn't make it into a 2.0.x release.
Basically you setup the VPN in tap mode, no tunnel network, set it to bridge to LAN, set the DHCP options you want, and then you have to assign the VPN interface under Interfaces > (assign), enable that, then setup an actual bridge between the LAN and that new interface.