There's an update to this article on Pro Video Coalition, Set Matte: a 32-bpc node for After Effects, which unlike Track Matte lets you use one matte on multiple layers.
Many people don't seem to know the Set Matte effect plug-in exists, maybe because it officially
exists only to provide compatibility with earlier projects. That seems
to have changed since Set Matte was upgraded to support 32-bpc color
depth in After Effects CS6...