Objects Sharing Shape Keys

So i’m making a model for source filmmaker and want to use shape keys. My problem is that i have eyebrow piercings that are separate objects to the body and wondering how to make them share a shape key.

I read this from the wiki "

  • Shape keys are part of the ObData datablock (i.e. mesh, curve, etc.), not of the Object one. Thus, it is possible to permit multiple objects to share the same shape keys by simply making them use the same mesh (or curve, surface, etc.) datablock. This applies to both the shape keys themselves, and to their Ipo animation (i.e. Shape Ipo curves)."

But it doesn’t say how to merge the datablocks. I tried googling but over an hour later still havent figured it out.

Any help appreciated.