Any OC potential for your locked CPU depends upon the mother board you use more than anything else. If your board provides Turbo multipliers for your CPU beyond 39, then you likely can use them.
Intel has set limits for many of the parameters that affect any OC potential, including the multiplier settings, and the less well know power duration settings. For example, the Turbo boost OC, whether standard (3.4GHz - 3.9GHz) or a higher top multiplier (39+) is not supposed to operate indefinitely, there is a time limit setting that the user cannot change. Mother board manufactures have found they can ignore the limits safely, and they are not enforced by Intel. If the limit for the max Turbo OC for your CPU (39) can be increased by the BIOS/UEFI, and accepted by the CPU, and a manufacture includes that on their board, it will work. As you've read, some manufactures are doing that now for non-K CPUs.
I know ASRock is one manufacture that does that, adding "non-K" OC to some of their Z77 chipset boards. You can possibly find more is you look.