Just updated to Kernel 4.2.2, and the long-standing NVIDIA GPL-only issue is finally fixed..

From the changelog:

commit 4f7760e963db10618dd3617bcf6254d896094e37
Author: Tim Gardner <tim.gardner@canonical.com>
Date:   Tue Aug 4 11:26:04 2015 -0600

    workqueue: Make flush_workqueue() available again to non GPL modules

And I can confirm that NVIDIA 355.11 compiles OK, without any patches..

The complete changelog is here: https://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.2.2

Robert Gadsdon   September 29, 2015.