Redirect user on first visit based on geographical location

I would say use a $_SESSION['var'] var or $_COOKIE[] to check if the link is clicked. Looks like the plugin is calling the geo_redirect_client_location function and then redirecting.

function geo_redirect_client_location(){
    $geo = new Geo_Redirect();
    $geo->checkIfRedirectNeeded();
}

I’m not familiar enough with the plugin but I would so something like:

<a href="https://wordpress.stackexchange.com/questions/89111/example-intenational-sitelink.com/?show_intl=true">Link on US site to show Intl site</a>

Then on the intl site:

If(isset($_GET['show_intl']) && $_GET['show_intl'] == "true"){
//set our cookie or session data here
}

Then modify/fork the plugin (or find the right hook)

function geo_redirect_client_location(){
if(!isset(Cookie or Session){    
    $geo = new Geo_Redirect();
    $geo->checkIfRedirectNeeded();
}
}

Basically this is just an overview of how I’d do it. You’ll have to do you’re own digging into the code to get it to work right