The hospital is dead easy to get into - multiple points of entry, public place, hell - we could walk right up to his ward without a second glance in our civvies.
Get there with a dedicated healer (Yuma or Rin would be handy) hopefully while he's asleep, (but that can be worked around), witchified-grief disguise (with face/head covering, padding, voice modulator to protect our identity?) approach, quick-heal, and leave (undisguising in nearby toilets/changeroom at earliest opportunity).
Hitomi may be a little harder, but cooperation with Sayaka means that she could open a window/door for us. Disguise, sneak in, sleep heal, sneak out.
Now, Kyousuke probably needs a full heal (hence dedicated healer for speed) and he can deal with the miracle as he did in Canon. As for Hitomi, her injuries will heal normally (they aren't as severe as his were) so if we didn't want to do a full heal in order to preserve the masquerade for her, then we could do a few partial healing sessions just to move things along a little faster than otherwise (and thus we wouldn't need a dedicated healer) .
The main threat would then be the patient waking up/already being awake during healing - a stranger in weird clothes breaks into their room in the dead of night with glowing hands - they'd be hopping aboard the trauma train at Home Invasion Station and getting off at Justifiable Paranoia-ville. If we knew someone or had some way of keeping them under (Hypnosis, sleep powder, sing, yawn, <Insert soporific skill of choice here>) then I'd say we were golden.
Someone else walking in is also an issue, but having Sayaka as a spotter/excuse-maker in Hitomi household would make that place reasonably secure against nosy parents. As for the hospital - he's got a private room, so we could close the door and make a grief barricade or perhaps be spotter at the door while dedicated healer works.
As for emergency exits, Kyousuke's window is fairly huge: make sure to open it before healing, then a flying tackle-hug to healer out the window and fly away - too easy. Not sure about Hitomi, but window may not be a possibility there....
Grief Invisibility Cloak? *shrug*