How to set rowspan and colspan values on gwt Grid cell containing a widget?

let's say I have a code like this

Grid g = new Grid(2,2);
Label l = new Label("Hello");
g.setWidget(0,1, l);
s.setColspan(0,1,2); // there is no such method :(

So how can I set rowspan and colspan values on gwt Grid cell containing a widget?