Set up a job with parameters that does a single "Publish Selenium Report" at the end.
Then set this job to "Execute concurrent builds if necessary".

Now run this job concurrently with different parameters.

If 3 concurrent builds are running, then all 3 builds will block until all 3 builds are complete to publish the selenium report.

i.e. if build 1 takes 5 minutes, build 2 takes 2 minutes, and build 3 takes 9 minutes - build 1 & 2 will wait until build 3 is done to publish the selenium report on all 3 builds.

Ideally, this shouldn't block at all, and let concurrent builds kick through.