I too have found the issue of scaling consulting to be insurmountable, but there are others who have succeeded. One key factor would be to take someone, no matter how junior and start charging for him at least the normal if not senior rate straight away - that way this is profitable from day 1. I was never brazen enough to do it and training people off project for free doesn't generally happen anywhere else so it's a huge disadvantage - start charging from day 1 (or don't hire if you can't).