Setting up a dependency as a module

I try to factor my projects into smaller sbt-based modules. Then it happens often that I am working on a project A and need to change code in one of the dependency projects (call it X). I don't want to simply edit X in its own idea project and do `publish-local` each time, but I want to have the source code for both projects inside the same Idea project.

How can I achieve this in a simple way? I tried importing the X as a new sbt-module (by doing `add module`). Then Idea works for a little bit (telling SBT stuff on the status bar), but in the end it somehow failed, and I see no new module. But Idea asks me whether I want to remove the CVS content root for the removed project X.

Once, after much manual fiddling, I managed to setup project X manually by specifing source directories and copying library xml files around. And after reopening, Idea simply correctly imported the sbt-based project X into the project (fixing the test dependencies, which I omitted during the manual setup). So somehow it must be (nearly?) working.

So:
- Is this functionality supposed to work right now? If so, how can I import another sbt-project as module?
- If this is not implemented, I'm now asking to implement it, since this is a much needed functionality for me. (And I suppose for others, too).