Page Navigation - Link vs Page when appending a query string to the result

[Joel Halbert]

I want to return the user to a page that has a context and some query 
params:

I can do this, using Link:
    public Object onSubmit(){
        Link link = ls.createPageRenderLinkWithContext(Buy.class, product);
        link.addParameter("x", x);
        link.addParameter("y", y);
        return link;
    }

Directs the user to;
http://localhost:8080/web/buy/product?x=1&y=2

I want to know if I can easily do the same using Page:

    @InjectPage
    private Buy buy;
    public Object onSubmit() {
        buy.setProduct(product)
        return buy;
    }

And in Buy have an onPassivate to get the correct context
Buy {
    String onPassivate90{return product}
}

Whch gets me the URL:
http://localhost:8080/web/buy/product

But what's the easiest way of then tacking on the query string I want?