Have you considered thread grafting some roots? Granted, I am brand new to bonsai, but I've read about it and last night in my introductory bonsai class I saw some slides of it. It seems to be an effective (and really neat) way to increase attractive nebari on your tree.
Oh! Just found this link
http://www.bonsai4me.com/AdvTech/AT...aftingroots.htm