In post.html

<!-- In the HTML of your posts: Replace ID number with ID of your gist -->
<p class="embed_gist"><a href="http://gist.github.com/367154">http://gist.github.com/367154</a></p>

Theme HEAD.html

<!-- uses jQuery -->
<!-- cannot find original JS code source, but I didn't write it -->

    {block:IfGitHubGists}
    <script type="text/javascript">
    //<![CDATA[
    $(document).ready(function() {
        var gist_injectors = $.map($('p.embed_gist').get(), (function(p){
            return function(){
                gist_injectors.shift();
                var atag = $(p).find('a:first');
                var gist_id = atag.attr('href').replace(/.*gist.github.com\//g,'');
                document.write = function(gist_style_link){
                    $('head').append(gist_style_link);
                    document.write = function(gist_html){
                        $(p).replaceWith(gist_html);
                        if (gist_injectors[0]) gist_injectors[0]();
                    };
                };
                if(gist_id.match(/#/)){
                    gist_id = gist_id.substr(0, gist_id.indexOf('#'));
                }
                if(!gist_id.match(/.js/)){
                    gist_id += '.js';
                }
                if(atag.attr('title')) {
                    gist_id += '?file=' + atag.attr('title');
                }
                $(document.body).append('<scr'+
                    'ipt src="http://gist.github.com/'+gist_id+'"></scr'+
                    'ipt>');
            };
        }));
        if (gist_injectors[0]) gist_injectors[0]();
    });
    //]]>
    </script>
    {/block:IfGitHubGists}
    
    <meta name="if:GitHub Gists" content="0"/>