I sign my name to this feature request as well.
We should have an option to either put an aircraft on storage or mothballing. Currently, the only way to do this is either scrapping or listed the aircraft for sale. Most of the times, scrapping is not an option. And listing an aircraft can backfire once the airline cancels/returns the aircraft to you. Thus, it "enters" the fleet again were by you get charged fleet comm costs for it.
Again, when you have the time, if you could look into these options.