Happily, some actual scientific research has been done into reducing the CD of the A2 by 3 well respected universities in the UK.
here's some slides from the University of Warwick that managed to reduce the drag efficiency of the already slippy A2 by 33%
https://warwick.ac.uk/fac/sci/wmg/re...view_may11.pdf
https://warwick.ac.uk/fac/sci/wmg/re...tion120221.pdf
Plenty potential ideas there ( may be worth exploring when it comes off the daily crawl through rush hr traffic with the Burd)