Unset environment variable starting with =

Question

I have this stange environment variables in my windows (discussed here and here):

C:\Users\******\Desktop>set ""
=::=::\
=C:=C:\Users\******\Desktop

Unfortunately, I have to run a software that trips over this (Apache Spark). Because filing an issue there (or at Java, because the people at Spark claim it's Java's fault) would take too long, I'm looking for a temporary solution to remove these environment variables.

Because they contain more than one =, my first approaches using setx or set XY= failed. Is there any solution for this?

Because I also run bash with cmder.exe (where the variable looks like that: !::=::\), a solution using bash utilities would also be acceptable.

Update: I temporarily circumvented the problem by calling the Spark start script from Bash on Ubuntu on Windows. The environment variables of the host system aren't set there. However, I don't consider this a permanent solution.