If you look at the Portfolio Settings (located at the bottom of the Genesis Theme Settings page) you’ll see – “Select one of the following:” you can change that to “Display Post Content” and then add a number to the “Limit Content to:” section. This is how I have it setup in the demo.
You can also take a look at this StudioPress tutorial/code snippet page to see how to add/modify the read more links – http://my.studiopress.com/snippets/post-excerpts/#content-more-link ….once you do this, all you have to do is add css to it which is what makes it into a “button”. Take a look at your css file on or around line 885 and you’ll see an example of where it is already done – “#content .portfolio .more-link“. Also, the code from this tutorial is already being used on the page_portfolio.php file, so if you add it again you’ll need to change the function name or it will give a duplicate error.
I created buttons that you can add anywhere manually if you want, you can see them here at this link – http://demo.appfinite.com/optimal/buttons-boxes/ ….the code is at the bottom.
You may have already seen some of this but I thought I’d share just in case.
Let me know if that works.