MSM wide global variables

I think I already know the answer to this but I just want to be sure…

I’d like to have Global Variables that are editable as such inside the EE interface that are global to all sites running under an MSM enabled installation but it seems this is not possible; they are only ‘global’ to a site.

I love the fact that Snippets can be installation wide, available to all sites. Is there any way this can be applied to global variables so that they are truly, er, global?

If not, I guess I can use a Snippet as if it were a Global Variable but presumably that’s not quite as efficient?