I have created an article for implementing this custom action button you need:
http://www.fop2.com/blog/creating-a-cus ... ion-button
There are a couple of fixes that I have to make in the fop2.js file to avoid duplicate commands upon a server reload, that will be incorporated on FOP 2.25. Anyways, this will work on fop 2.24 too. I will release 2.25 in a few days.
Best regards,