IIRC it's telepathy-ofono that wakes the screen up for this still (I know, not the greatest architecture...), and powerd/u-s-c are responsible for actually turning it on and off based on proximity. So, as long as the screen is kept on with proximity enabled by telepathy-ofono, u-s-c and powerd should do the right thing and check proximity before turning the display on.
IIRC it's telepathy-ofono that wakes the screen up for this still (I know, not the greatest architecture...), and powerd/u-s-c are responsible for actually turning it on and off based on proximity. So, as long as the screen is kept on with proximity enabled by telepathy-ofono, u-s-c and powerd should do the right thing and check proximity before turning the display on.