I can get the 'someMethod()' auto inserted by typing c. then hitting ctrl-space.
How about putting the cursor at the start of the method call and hitting ctrl-space, and having an intention popup: "Assign return value to variable"
This would insert something like:
Map> aVariableName = c.someMethod();
or maybe based on a config setting do this: (split assignment and declaration)
Map>]]> aVariableName = null;
aVariableName = c.someMethod();
I had a quick look around the menus and didnt see any options that looked like they would do this - if IDEA can do this now, please point me in the right direction.