Before you reply: this is not as straight foward as you\'d expect!
thanks for pointing me in the right direction Andrew, my problem was that the callback in the api request is mandatory for loading the api on demand.
Here is my final jquery code:
//in doc.ready
$('img.map').click(function(){
var rel = $(this).attr('rel');
$('body').data('map_href', rel ).append('');
})
function show_map(){
$.fn.colorbox({
href:$('body').data('map_href')
})
}