There will new item on BPEL palette: JavaScript.
D'n'd of the item will create empty extension assign operation:
On diagram the extension assign will have own icon.
Double click on the extension assign will open JavaScript dialog. It will have components to set input and output expressions, and text area for JavaScript code.
Input and output buttons will show table with mapping between BPEL and JavaScript variables.
Next dialog is to specify BPEL and JavaScript variables, it will be opened on clicking on Add and Edit buttons.
http://wiki.open-esb.java.net/attach/Referenced_Resources_Help/pic_01.gif
This is the draft of UI and dataflow for embedded JavaScript functionality, so UI is not final and can/should be changed and improved.