How to create subsystems with electrical signals in Simulink?

The standard subsystem blocks I've found only allow for simulink signals to be passed into and out of the subsystem. I'm trying to group circuits into blocks of some kind to prevent my designs from becoming unmanageable. The problem I'm running into is I can't find any grouping block or subsystem that allows for electrical simelectronics signals to pass through, such as power or ground wires. If anyone knows a way around this or a helpful way of grouping the circuits it would be greatly appreciated. I'm using 2013a.