Put up posters on all the lamp-posts along that stretch pointing out that the highways authority have chosen do accept joint liability of any doorings that occur by deliberately creating the hazard, and giving postal and email addresses for the highways authority, as well as telephone numbers.
Replace as necessary.
Lamination makes them last longer, as will the use of heavy duty non-releasable cable ties.
FOI the highways authority for the name of the person responsible for placing them there, and the details of their professional indemnity insurance coverage (they'll be needing it).
Research all cases of doorings and copy them to the highway authority, placing particular emphasis on those which have occurred in door-zone cycle lanes.
Send them a link to the Youtube video shot by the New York cyclist who was (wrongly) fined for cycling outside the cycle lane (Google should find it).
Never mind - it's here:
View: http://www.youtube.com/watch?v=bzE-IMaegzQ
Nearly 5 million views on it now.