The UI can't be color managed/controlled via the application. That's why when you load a soft proof and turn on the paper simulation, you should be editing in full screen mode (hit F key until invoked). Its explained on page 97/98.
An important consideration when using Simulate Paper Color is to
ensure that no other user interface items, such as palettes, are seen onscreen
when viewing the document. These items do not undergo the
paper white simulation so their whites are as bright as the display can
produce. Your eye will adapt to the brightest white of the monitor white
rather than the simulated white you see when the Simulate Paper Coloroption is on.
Therefore, when you want to view the document with Simulate
Paper Color simulation, view the document in full screen mode and
with a black background and no rulers showing. Press Tab to hide all the
palettes and then press “F” until the entire image is surrounded by a black
The UI in say Lightroom is far kinder to this kind of work. I hope in LR3.0 we get it, then it will be THE place to apply such edits (since they are metadata only) and we have that fantastic print module. Photoshop's idea of a print workflow is seriously lacking.