Take a dummy organization that is used to avoid taxes. There is nothing illegal to pay someone to form a company located in a different country. A company can also sell assets to an other for what ever price they want, and there is nothing illegal to declare that as a result one of the companies now have zero profits and zero assets.
But if something is legal or illegal depend more than just on each set piece. If combining a blob with the kernel creates a derivative, then just adding a shim to the mix won't turn it legal. Judges are trained to look at the big picture rather than the individual parts, and this is especially true in civil-law. Court systems are generally interested in:
What is the kernel authors intention by their copyright license.
What is the blob authors intention by their copyright license.
What is the distributor intention when combining the two works and what understanding did the distributor have about the other copyright authors and their wishes in regard to derivatives.
The existence of a shim that has no other purpose is a sign that something shady is going on, similar to dummy organizations. The question a judge is likely to ask is why such obfuscation was used since that can help establishing intention. If the end result is a de-facto derivative, and the intention was to create a single work out of two seperate works, and the creator knows that they are not allowed to create a derivative work, then a shim is not going to save the day.