Just did a bit more research. There's a B&M kit for the Z4M, but it vibrates/rattles at higher speeds, and is very stiff to get into gear.
Then there's the UUC SSK model #: USSZ43 which costs $325 +
I think they have a selector rod option coming out soon, but will probably cost another arm or leg
And then there's the Rogue Engineering Octane SSK for $165, but I don't think it has the selector rod, and I'm asking forum vendor EAS if it'll fit the Z4M.