Removing the spoiler all together would be my advice to but really it should be working. If it came to me the brake light forms part of a body panel which can be removed but as it's a factory fit item i'd class it as not technically an "Additional" brake light.
Stop being tight and just replace the bloody thing as they're a huge £23. Besides, a Policeman will just hand you a defect notice if you ball round with it not working.