You can merge multiple target shapes belonging to the same blend shape using the 
		
Shape Editor. Note that doing this removes keys on all the targets involved. To avoid losing data, duplicate any keyed targets first and hide them, then perform a merge with the originals. 
	 
To merge target shapes
- In the 
		  Shape Editor, select multiple target shapes belonging to the same blend shape. 
		
- Right-click any of the target shapes and select 
		  Merge Targets. 
		  Maya merges the selected target shapes to a single target shape.