LaTeX with biblatex and biber: How to balance \printbibliography in a two column IEEE trans paper?

I don't use that class, so I may have misunderstood your question. But I think you should be able to do something like this, in your preamble

\renewbibmacro{finentry}{%
  \iffieldequalstr{entrykey}{KEY}%<- key after which you want the break
   {\finentry\newpage}
   {\finentry}}

Instead of giving the reference by number, you give the key of the entrytype after which you want to insert \newpage (in the place where I have KEY in the macro above). Of course, you can add anything else you want here. Basically, the code you put in place of \newpage will be executed after the entry in question has been printed.

Based on Paul's answer, this is a drop-in replacement for the \IEEEtriggeratref macro that works with biblatex:

\usepackage{ifthen}

\makeatletter
\newcounter{IEEE@bibentries}
\renewcommand\IEEEtriggeratref[1]{%
  \renewbibmacro{finentry}{%
    \stepcounter{IEEE@bibentries}%
    \ifthenelse{\equal{\value{IEEE@bibentries}}{#1}}
    {\finentry\@IEEEtriggercmd}
    {\finentry}%
  }%
}
\makeatother

The usage is the same as the original macro:

\IEEEtriggeratref{9} % Breaks the column after the 9th entry
\printbibliography