The problem is that the license assigned says that anyone is free to use the code. Anyone is a set of people that includes the contributor, which then triggers the interpretation that the research is incrementally in the contributor's benefit and thus disqualified from preferential tax treatment.
You'd need a custom license where everyone in the world could use the results except for the contributor, and then like, a source control system that hides the source files from the contributor's view of the repository.