All of the answers address the question posed in the title. However, I would like to add a caveat that is implicit in the text. Bézier patches are used to represent the surface, but you cannot just transform the points of the patch and tessellate the patch into polygons, because this will result in distorted geometry. You can, however, tessellate the patch first into polygons using a transformed screen tolerance and then transform the polygons, or you can convert the Bézier patches to rational Bézier patches, then tessellate those using a screen-space tolerance. The former is easier, but the latter is better for a production system.
I suspect that you want the easier way. For this, you would scale the screen tolerance by the norm of the Jacobian of the inverse perspective transformation and use that to determine the amount of tessellation that you need in model space (it might be easier to compute the forward Jacobian, invert that, then take the norm). Note that this norm is position-dependent, and you may want to evaluate this at several locations, depending on the perspective. Also remember that since the projective transformation is rational, you need to apply the quotient rule to compute the derivatives.