General ⇒ humannat an extra indentation

[nerdyyatrice]

I am trying to use the latex BibTeX-style-file "humanbio.bst" . It is the only anthropology style file I can find and it is very helpful. The only problem is according to AAA, the third line((below the year)) of a citation should have an additional indentation. I tried to modify the .bst file but I am lost in all the symbols. I wonder if anyone know how to do that? Thank you very much.
Here is an example
Foster, I. and C. Kesselman
(tab)1999. The Grid: Blueprint for a New Computing Infrastructure. Morgan
(tab) Kauffmann Publishers, Inc.

what I need is
Foster, I. and C. Kesselman
(tab)1999. The Grid: Blueprint for a New Computing Infrastructure. Morgan
(tab)(tab) Kauffmann Publishers, Inc.

Help!!