Special handling for evgen MP

In evgen we need to handle MP a bit differently. This is my attempt, which seems to avoid errors in the transform itself. The problem is that we normally disable MP during the job, so that the output file appears as just a simple output file with whatever name has been assigned by the transform. There aren't a bunch of workers. Very happy to have input on whether there's a better way to do this!

In case they want to comment, tagging: @tsulaia , @mavogel , @ewelina , @lcorpe