I think he wanted to send Locke to the hospital. There, Locke meets Jack (again). And I bet Sun and Jin will go to the same hospital since Sun was shot. That's what I'm thinking too. And Desmond seems like he's immune to fake Locke's charm, which is probably why he threw him down the well, that and the fact that Widmore was using Desmond's ability to withstand electromagnetism to take out the smoke monster.