Anybody knows how to lock the back reference at the top left corner of the bibliography entry by employing BibTeX? The result should be like this:

It works to me when using \bibitem (yes, it goes there automatically) but not through a .bib file.
Here it is my code:
\documentclass[a4paper,12pt]{book}
\usepackage[spanish]{babel}
\usepackage[T1]{fontenc}
\usepackage{latexsym}
\usepackage{lettrine}
\usepackage[latin1]{inputenc}
\usepackage{setspace}
\spanishdecimal{.}
\usepackage[usenames,dvipsnames]{xcolor}
\usepackage{eso-pic}
\usepackage{everyshi}
\usepackage{pdfpages}
\usepackage[round]{natbib}
\bibliographystyle{plainnat}
\usepackage[backref=page,citecolor=MidnightBlue,linkcolor=MidnightBlue]{hyperref}
\hypersetup{colorlinks=true,plainpages=false}
\usepackage{etoolbox}
%backref edit. this part is thanks to [lockstep](http://tex.stackexchange.com/questions/36307/formatting-back-references-in-bibliography)
\makeatletter
\patchcmd{\BR@backref}{\newblock}{\newblock p.~}{}{}
\patchcmd{\BR@backref}{\par}{\par}{}{}
%all-in-one hyperlink ([D.Roepo](http://tex.stackexchange.com/questions/115039/single-link-in-author-year-citation-style-using-natbib-and-hyperref))
\pretocmd{\NAT@citex}{%
\let\NAT@hyper@\NAT@hyper@citex
\def\NAT@postnote{#2}%
\setcounter{NAT@total@cites}{0}%
\setcounter{NAT@count@cites}{0}%
\forcsvlist{\stepcounter{NAT@total@cites}\@gobble}{#3}}{}{}
\newcounter{NAT@total@cites}
\newcounter{NAT@count@cites}
\def\NAT@postnote{}
% include postnote and \citet closing bracket in hyperlink
\def\NAT@hyper@citex#1{%
\stepcounter{NAT@count@cites}%
\hyper@natlinkstart{\@citeb\@extra@b@citeb}#1%
\ifnumequal{\value{NAT@count@cites}}{\value{NAT@total@cites}}
{\ifNAT@swa\else\if*\NAT@postnote*\else%
\NAT@cmt\NAT@postnote\global\def\NAT@postnote{}\fi\fi}{}%
\ifNAT@swa\else\if\relax\NAT@date\relax
\else\NAT@@close\global\let\NAT@nm\@empty\fi\fi% avoid compact citations
\hyper@natlinkend}
\renewcommand\hyper@natlinkbreak[2]{#1}
% avoid extraneous postnotes, closing brackets
\patchcmd{\NAT@citex}
{\ifNAT@swa\else\if*#2*\else\NAT@cmt#2\fi
\if\relax\NAT@date\relax\else\NAT@@close\fi\fi}{}{}{}
\patchcmd{\NAT@citex}
{\if\relax\NAT@date\relax\NAT@def@citea\else\NAT@def@citea@close\fi}
{\if\relax\NAT@date\relax\NAT@def@citea\else\NAT@def@citea@space\fi}{}{}
\makeatother
\usepackage{float}
\usepackage{epstopdf}
\usepackage{amsmath,amsbsy,amsfonts,amssymb,amscd,fancyhdr}
\DeclareGraphicsExtensions{.jpg,.pdf,.png,.gif,.eps}
\usepackage{rotating}
\usepackage{longtable}
\usepackage{chngpage}
\usepackage{anysize}
\usepackage{geometry}
\usepackage{aecompl}
\newcommand\BackgroundPic{
\put(0,0){
\parbox[b][\paperheight]{\paperwidth}{
\vfill
\centering
\vfill
}}}
\begin{document}
As it is said in \citet{trigo00} and \citet{venus}...
\mainmatter
{\refname}
\addcontentsline{toc}{part}{Bibliografía}
%%%%%%%% B1 (bibliography according to bibitems) %%%%%%%%%%%%%%%
\begin{thebibliography}{999}\bibliographystyle{plainnat}\label{biblio}
\bibitem[Svedhem et al.(2007)]{venus}
Svedhem, Hakan; Titov, Dmitry V.; Taylor, Fredric V.; Witasse, Oliver (2007). ``Venus as a more Earth-like planet''. Nature 450 (7170): 629-632.
\bibitem[Trigo y DaCamara(2000)]{trigo00}
R. M. Trigo and C. C. DaCamara, ``Circulation weather types and their influence on the precipitation regime in Portugal'', {\em International Journal of Climatology}, vol. 20, pp. 1559-1581, 2000.
\end{thebibliography}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%% B2 (Bibliography according to Bibtex) %%%%%%%%%%%
% \bibliography{my_bib_file}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{document}
my_bib_file.bib:
@article
{venus,
title={Venus as a more Earth-like planet.},
author={Svedhem, H. and Titov, D.V. and Taylor, F.W. and Witasse, O.},
journal={Nature},
volume={450},
number={7170},
pages={629-32},
year={2007},
}
@article {trigo00,
author = {Trigo, Ricardo M. and DaCamara, Carlos C.},
title = {Circulation weather types and their influence on the precipitation regime in Portugal},
journal = {International Journal of Climatology},
volume = {20},
number = {13},
publisher = {John Wiley & Sons, Ltd.},
pages = {1559--1581},
keywords = {atmospheric circulation variability, droughts, Portugal, precipitation, weather typing},
year = {2000},
}
If B1 is commented and B2 enabled, the backref goes to the end of the bibliography entry, like this (I need the format at the top but with BibTeX):
