How does this apply given that we're assuming Google has enough cash on hand from profit of other aspects of their business that they do not finance most projects through new loans (debt) from banks at current interest rates because they don't need to?
Their cash balance doesn't really matter, it impacts their cost of capital in various ways, but you can still compare the ROIC of any given project to the overall company's cost of capital.
E = equity value
D = debt value
Ke = cost of equity
Kd = cost of debt
T = tax rate
Ke = Rf + B * ERP
Rf = risk free rate
B = beta of company
ERP = equity risk premium
Kd = Rf + credit spread
In theory, if a project's ROIC is less than WACC, it does not generate economic value.