How to Setup Global Site Tags and Search not on the Main Site

Hi. I've kind of half asked this same question at the end of another thread here:
but thought I'd start a new one as its a fresh question.

On our multi-site install, we want to create a site called search.oursite.com and run both the global search and global tags from there instead of our main site.

Can this be done? If so, what code do I need to change?
I'm assuming it's something like this in wp-config:
define( 'GLOBAL_SEARCH_BLOG', 18 ); or something like that.

thanks in advance