You cannot do (a good) anti-aim externally. You should fake the viewangles sent to the server on CreateMove and/or take advantage of the fact that your headhitbox and your view/camera offset are not the same.
EDIT: I should clarify... is it possible to do it externally? Probably... Should you do it externally? No. I dont think ti's worth the hassle. If you want anti-aim might as well go internal and do it properly.