Is a Grsec enabled kernel a possibility?
I guess if it was trivial it would already exist, but I'm pretty sure quite a few of us would appreciate it.

Is this possible yet?

I didn't see the /proc entry on the 2.6.18.8-linode10 kernel. According to the OpenVZ wiki 2.6.18-028stab047.1 and later versions have this ability.

Linode uses Xen (and UML on older hosts), not OpenVZ.

It's currently possible in theory I suppose, with very experimental software not yet ready for production use in any way (I speak of pv-grub).

With kernels supported by Linode, there is no grsec support.

So, no, it's not possible/feasible at this time.