\begin{tikzpicture}
 % explode list
 \pie[explode={0, 0, 0, 0.1}] {10/A, 20/B, 30/C, 40/D}

 % explode all
 \pie[pos={8,0}, explode=0.1] {10/A, 20/B, 30/C, 40/D}
\end{tikzpicture}