How might I use a plugin function site-wide if the plugin isn't active site-wide?

Hi folks,

I’m running a multisite install for which I have a plugin that I do not necessarily want to run network-wide. It is used on the main site, and may be used on child sites in the future. BUT, there is a feature of the plugin – it’s WPML to be specific – that I need to appear everywhere. And, of course, for sites where the plugin isn’t used I get a “Fatal error: Call to undefined function”.

Basically I want my language indicators to appear network-wide without activating the plugin network-wide. Am I dreaming? Is there a way? I thought using the blog switcher would be enough, but that doesn’t seem to work. Even though the language switcher is within the part of the header that uses

global $switched;

I still get the error.