It's best if he be asked to leave. It's really as simple as that. He should have learned what's expected in the position that he has. With luck, losing this position will be a wake-up call for him to get his head together.

Trying to minimize the pain for him by keeping him around isn't going to do him, or your organization any good. He needs to be somewhere else to think about what it means to work because the pain of losing a job later is much more intense.

I would only suggest keeping him around if you have some-sort of internship program where he would be heavily supervised with the strong message that he needs to shape up quickly. But if there isn't a spark somewhere that indicates that he's going to grow into the job, well I think for his sake and yours that you need to have him move on.

My $0.02.

Cheers,
Scott.