I think it may be possible, but I’m not 100% sure. Think of the portfolio template as a Blog that displays your posts in a “portfolio” format. I think the only way to manually do it, is to copy the html/source code from the portfolio page (as an example), then add that code in a page….then replace the text/images with whatever you want. I haven’t tested this myself, but I think it should work if you add the same html code that is used on the portfolio template.
For example, here is the exact code from the portfolio page on the demo –
<article class="post-1 post type-post status-publish format-standard category-uncategorized entry portfolio gallery clearfix" itemscope="itemscope" itemtype="http://schema.org/BlogPosting"><header class="entry-header"><a href="http://demo.appfinite.net/epik/2013/08/13/hello-world/" title="Hello world!"><img width="264" height="200" src="http://demo.appfinite.net/epik/wp-content/uploads/2013/08/wlambo-264x200.jpg" class="alignnone post-image" alt="Capristo Lamborghini Aventador Carbon"></a></header><div class="entry-content" itemprop="text"><h1 class="entry-title" itemprop="headline"><a href="http://demo.appfinite.net/epik/2013/08/13/hello-world/" title="Hello world!" rel="bookmark">Hello world!</a></h1>
<p>Welcome to WordPress. This is your first post. Edit or delete it, then start blogging!
This is an <a class="more-link" href="http://demo.appfinite.net/epik/2013/08/13/hello-world/" rel="nofollow">Read More</a></p></div><footer class="entry-footer"></footer></article>
<article class="post-20 post type-post status-publish format-standard category-category-1 tag-threaded-comments entry portfolio gallery clearfix" itemscope="itemscope" itemtype="http://schema.org/BlogPosting"><header class="entry-header"><a href="http://demo.appfinite.net/epik/2013/05/01/threaded-comments/" title="Sample Post With Threaded Comments"><img width="264" height="200" src="http://demo.appfinite.net/epik/wp-content/uploads/2013/08/stevejobs-264x200.png" class="alignnone post-image" alt="stevejobs"></a></header><div class="entry-content" itemprop="text"><h1 class="entry-title" itemprop="headline"><a href="http://demo.appfinite.net/epik/2013/05/01/threaded-comments/" title="Sample Post With Threaded Comments" rel="bookmark">Sample Post With Threaded Comments</a></h1>
<p>This is an example of a WordPress post, you could edit this to put information about yourself or <a class="more-link" href="http://demo.appfinite.net/epik/2013/05/01/threaded-comments/" rel="nofollow">Read More</a></p></div><footer class="entry-footer"></footer></article>
<article class="post-18 post type-post status-publish format-standard category-category-1 tag-images-left entry portfolio gallery clearfix" itemscope="itemscope" itemtype="http://schema.org/BlogPosting"><header class="entry-header"><a href="http://demo.appfinite.net/epik/2013/05/01/image-aligned-left/" title="Sample Post With Image Aligned Left"><img width="264" height="200" src="http://demo.appfinite.net/epik/wp-content/uploads/2013/08/niceworldmap-264x200.jpg" class="alignnone post-image" alt="niceworldmap"></a></header><div class="entry-content" itemprop="text"><h1 class="entry-title" itemprop="headline"><a href="http://demo.appfinite.net/epik/2013/05/01/image-aligned-left/" title="Sample Post With Image Aligned Left" rel="bookmark">Sample Post With Image Aligned Left</a></h1>
<p>This is an example of a WordPress post, you could edit this to put information about yourself or <a class="more-link" href="http://demo.appfinite.net/epik/2013/05/01/image-aligned-left/" rel="nofollow">Read More</a></p></div><footer class="entry-footer"></footer></article>