It's a bit of a hack, but since the cell list is just a list of Divs, you can use the CSS3 columns (but watch out, IE9 doesn't support this, and only the most recent version of opera does)
public void setColumns(int columns) {
if(columns < 1) columns = 1;
Style style = cellList.getElement().getStyle();
String cols = String.valueOf(columns);
/* You could used deferred binding here if you weren't lazy */
style.setProperty("MozColumnCount", cols);
style.setProperty("WebkitColumnCount", cols);
style.setProperty("columnCount", cols);
}
public void setColumnPadding(int width) {
if(width < 0) width = 0;
Style style = cellList.getElement().getStyle();
style.setProperty("MozColumnGap", width, Style.Unit.PX);
style.setProperty("WebkitColumnGap", width, Style.Unit.PX);
style.setProperty("columnGap", width, Style.Unit.PX);
}