In our case, after sponsor approval we had the COPR anyways in only a couple months so just did the normal PR landing then 3 months wait for healthcare from that. So we never bothered to try (also since I just assumed it was impossible). However if people have done it on a visitor visa, I would ask them if its possible and how. Everything i've read on the "health" forum of this site seems to indicate it's for inland applications only.
You should definitely call them to try and confirm, but be prepared to jump through hoops and get lots of mis-information. Even if a customer service person on the phone says you can apply, the people at the Service Ontario offices for healthcards may feel differently. People on the phone often don't know the full situation, and may not understand CIC issues like inland and outland.