Id be surprised if after a season of football in that position he wouldn't be classed as 'accomplished'. I reckon a season after a half to 2 seasons in that position would see him become 'natural' to that position. I reckons after all that time though, it'd be pointless to retrain him there - granted he's a decent player, but there's already very good accomplished/natural AMLs out there; unless you have a certain love for the guy, which in that case go for it.
It was born out of me thinking that this is what Newcastle should do with him in real life, but if it's going to take so long and possibly at the expense of the team having him play there until he's accomplished I might not bother. I'm surprised he has absolutely nothing in the aml and amr or even ml and mr slots though.