Project Layout for supporting multiple IntelliJ IDEA versions

Hi, I asked this in my other thread, but I'm posting it now as separate question to maybe get attention by possible answerers that don't follow that other thread.

I want to have a plugin support incompatible versions of IntelliJ IDEA, e. g. being DumbAware in 9+ and not DumbAware up to 8 as this doesn't exist there.
I want to support this by having two separate versions of the plugin with different since-/until-build values.

Is there a suggested project layout for such a setup, or someone has made some experiences with such a situation?
One Module with common code and then multiple modules for the different versions that depend on the common module?
If so, what would be the type of the common module, also of Plugin type?
Or a Java module and the IntelliJ JARs as provided library?
Or even something completely different?          

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