Share shortlink instead of long URL

Hi there,

I apologize in advance if the answer is here somewhere, but I am not having any luck finding it.

I’m using a URL shortening service (YOURLS) that I have set up so that WordPress shortlinks are using it. I’d like AddThis to share the page’s shortlink instead of the perma-link. In the addthis_share values field in Advanced Settings, I’ve tried the following:

{
    "url": "<?php echo wp_get_shortlink(); ?>"
}

The validation is satisfied, but upon saving, the value is reduced to simply: { "url": "" }

How can I share shortlink codes if PHP code is not accessible in this field? Thanks in advance.

http://wordpress.org/extend/plugins/addthis/