They don't just create shadows they also seduce electronically generated tracks in most radar systems. Wake turbulence is well known and there are studies underway.
You may find this document useful.
http://www.caa.co.uk/docs/33/Cap764.pdf
From my perspective, the answer is to deploy multi-static primary surveillance radar, either passive or active. Not only does it free up spectrum but, as the system works in three dimensions, most of the problems could be mitigated by this system. Problem is, it is developing technology and will cost money to set up.