// unbind normal behavior. needs to occur after normal infinite scroll setup.
$(window).unbind('.infscr');
// call this whenever you want to retrieve the next page of content
// likely this would go in a click handler of some sort
$(document).trigger('retrieve.infscr');

<div id="items">
    <!-- Run your query using the page parameter to offset items, then display the items here -->
</div>
<button id="more">More</button>

var page = 0;
$('#more').click(function(){
    page++;
    $('<div/>').appendTo('#items').load('the/same/url/?page='+page+' #items');
});

$('.container').infinitescroll({
        // infinite scroll options
    },
    function(){
        // pause when new elements are loaded
        $('.container').infinitescroll('pause')
    }
);

function resume_infinite_scroll(){
    // resume
    $('.container').infinitescroll('resume')
    // check if new elements should be loaded
    $('.container').infinitescroll('scroll')
}

<button onclick="resume_infinite_scroll()">load more</button>