Apologies for such a late reply and I realize my response may be irrelevant to you at this point, but I wanted to respond if at least to thank you for your kind words.
Unfortunately, the organizational chart plugin I created is mostly an interface for users to be able to easily take advantage of the Google made Organizational Chart tool. As such, most of the actual code for creating the charts is part of the Google code found here: https://developers.google.com/chart/interactive/docs/gallery/orgchart
From what I understand, there is currently no feature provided by the Google tool to make the org charts in a horizontal format although it seems to be a commonly requested feature. You can take a look at this issue tracking thread as the feature may be completed sometime soon in the future: http://code.google.com/p/google-visualization-api-issues/issues/detail?id=47
If the feature is completed, you're welcome to notify me and I will try my best to add the feature to this plugin as well depending on my availability. However, due to my current time constraints, I am unable to create the feature myself.
The best I could do for now is recommend that you try to apply some CSS styling to your chart such that the box margins and the whitespace on your chart are minimized. A great plugin you can use to add CSS code can be found here: http://wordpress.org/extend/plugins/imporved-simpler-css/
Furthermore, if you are new to CSS, here is an excellent tutorial that can take you through the basics and will have you styling your webpage in no time: http://www.w3schools.com/css/ Google Chrome's developer tools can also help you take a look at your existing styling and you can play with values and see the changes in real time without the fear of accidentally changing something on your live website. Simply hit F12 in a Google Chrome browser to access the developer tools. (The Firefox equivalent is a plugin called Firebug.)
I want to thank you for your feedback, and I apologize that I cannot be of much help to you at this time. I wish you all the best and hope that you can find a solution that works for you. Lastly, if you discover that the feature has been added to the Google Organizational Charts, let me know and hopefully I will be able to add a quick fix to implement the feature.