Reverse engineering the GWT event handler code to add new events is simple. Here’s a Flex Table which also handles mouse events:

	/**
	 * Internal flex table declaration that syncs mouse down/move/up events
	 */
	private static class MouseFlexTable extends FlexTable implements HasAllMouseHandlers
	{
		@Override
		public HandlerRegistration addMouseDownHandler(MouseDownHandler handler)
		{
			return addDomHandler(handler, MouseDownEvent.getType());
		}

		@Override
		public HandlerRegistration addMouseUpHandler(MouseUpHandler handler)
		{
			return addDomHandler(handler, MouseUpEvent.getType());
		}

		@Override
		public HandlerRegistration addMouseOutHandler(MouseOutHandler handler)
		{
			return addDomHandler(handler, MouseOutEvent.getType());
		}

		@Override
		public HandlerRegistration addMouseOverHandler(MouseOverHandler handler)
		{
			return addDomHandler(handler, MouseOverEvent.getType());
		}

		@Override
		public HandlerRegistration addMouseMoveHandler(MouseMoveHandler handler)
		{
			return addDomHandler(handler, MouseMoveEvent.getType());
		}

		@Override
		public HandlerRegistration addMouseWheelHandler(MouseWheelHandler handler)
		{
			return addDomHandler(handler, MouseWheelEvent.getType());
		}
	}

Addendum:

If you want the location (the cell) in which the mouse event happened, you can extend MouseFlexTable with the additional methods:

		public static class HTMLCell
		{
			private final int row;
			private final int col;
			
			private HTMLCell(int r, int c)
			{
				row = r;
				col = c;
			}
			
			public int getRow()
			{
				return row;
			}
			
			public int getCol()
			{
				return col;
			}
		}
		
		public HTMLCell getHTMLCellForEvent(MouseEvent event) 
		{
			Element td = getEventTargetCell(Event.as(event.getNativeEvent()));
			if (td == null) {
				return null;
			}

			int row = TableRowElement.as(td.getParentElement()).getSectionRowIndex();
			int column = TableCellElement.as(td).getCellIndex();
			return new HTMLCell(row, column);
		}