I know that the package cuted can do its job quite well. However I'd be interested in different layout than what cuted provides. I hope that the image will be worth milion words:
On the left is the cuted output, on the right is what I would like to achieve.

Minimal example using the cuted package:
\documentclass[a4paper,twocolumn]{article}
\usepackage{cuted}
\usepackage{lipsum}
\begin{document}
{\bfseries PIECE 1 \lipsum[1]}
\begin{strip}\leavevmode\kern15pt
\begin{minipage}{\dimexpr\linewidth-30pt\relax}
{\itshape PIECE 2 \lipsum[2-3]}
\end{minipage}
\end{strip}
{\scshape PIECE 3 \lipsum[4-6]}
\end{document}