Prompt for merge message?

I often find myself using "--no-ff -m foo" for merging short-lived branches, because the merge commit usually needs to say something about having finished a feature rather than referring to a branch that will be deleted shortly anyway. However, it's a little annoying to have to always write the commit message on the command-line, especially in cases where a more expository multi-line message would be useful.

Is there currently a way to get git to prompt for the merge message, rather than using the default or requiring the -m flag? If not, isn't this a common-enough use case to have that ability added to the merge function?