Sincerely apologize for the late reply. I'm currently in the midst of a business trip with little access to the internet.
I didn't reply earlier also because I'm not familiar with joomfish and I do not have an answer for you.
I wrote the Include Content Item plugin, but NOT joomfish. As such, I'm not familiar with joomfish and I do not know where to change the code to do what you want to do.
If you look at the page where you download the plugin: http://www.kksou.com/php-gtk2/Joomla/Include-Content-Item-plugin.php
the integration with joomfish was actually contributed by one of the users, Dr. J.R.Halon.
You might want to try posting your question in the official Joomla forum (joomla.org). Someone else might already have a solution for it.
Alternatively, you can try to see if there's any other plugin in joomla.org that might already provide the same functionality that you need.