Create bridge interfaces with preseed

Hello,

i'm trying to provision a host with bridge-interface via preseed.

There are no variables to create an interface listed in
http://projects.theforeman.org/projects/foreman/wiki/templatewriting

Using @host.bond_interfaces for bondings works well but i can't find
variables for bridges.
I tried same procedure with @host.bridge_interfaces but that doesn't work.

Is there a way to realize it?