I have an example of how to add HAML/SASS converters to RubyMine editor.
It could be handy when you try to convert large legacy code from erb templates into haml templtes. Sometimes you need to convert fragment-by-fragment, not by complete file.
Also, it could be useful as an example for creating other ruby-plugins for RubyMine.
It also could give an insight to RubyMine developers what needs to be changed in order to make this task trivial (in case of multiple gem dependencies).
See details http://scriptlandia.blogspot.com.