You CAN switch to O1, if you have the credentials to get it approved. With 'pull' from a major university behind you, it is usually possible to get an O1 approved. But as the previous poster mentioned, this does not relieve your HRR. However, if you travel back to your home country frequently and for extended periods, you can fulfill your HRR piecemeal. (people in 'regular' academia outside of medicine do that at times. They will take 3 months off every summer to write some papers, go to conferences around the world while traveling through their home country etc. That way, you can get your HRR through in maybe 5 years. If you are a physician with the typical 4 week annual vacation, it will take you 24 years......)
What people at academic medical places will frequently do, is to switch a promising fellow to O1 and have him hang out for a year or two until a position at the affiliated VA hospital becomes available. The person transfers to the VA and serves out his sentence. After 3 years, a green-card is waiting at the main university hospital.