Well, not 100% exactly from WWJava, but GeoMapApp does have a feature that lets you load a spreadsheet, view the data on the WWJava globe and then export/save to several formats, you can save the entire table to KMZ or just a selection of data.
In the GeoMapAppVG application that I posted last week there is the ability to import a spreadsheet (as ascii table or in Excel format), view the placemarks in the map window ( GeoMapAppVG example) and then export the placemarks in a kml file using an interface that allows the user to choose which column or columns of the table are to be in separate folders in the kml file and how to scale the color of the placemarks in proportion to numeric values in the selected columns. The placemarks come up in GE scaled by color to the attribute chosen from the spreadsheet (Google Earth example). In the example the placemarks have been color-coded according to the percent CaCO3 in the sediment on the seafloor.
Edit: Forgot to mention, this is NOT using the libkml, this is an in-house developed solution for WWJava (that would be good to add to the core code as well).