How to support older versions of Unity?

I have an asset in the Asset Store which is fully supported in Unity 4.0. I want to support Unity 3.5 too, however there certain are lines of code that do not work in 3.5. This code is not mandatory for my asset to work, since it is only used in examples/demo's, and could easily be left out. How can I create my asset so that customers with Unity 4.0 or higher get a version of my asset which includes those certain lines of code, while this code is excluded for customers with Unity 3.5 (or lower)?