I just checked with FindBugs 2.01, and annotating methods with @CheckForNull and @Nonnull seemed to have the desired effect.
That being said, this appears to be a can of worms; JSR-305 is dormant; FindBugs supports the annotation using it's own package + javax.annotation.
IntelliJ is said to support them in "all" packages, but I can't test that.
There's also a Eclipse JDT extension in the works which appears to be configurable with respect to package names (http://wiki.eclipse.org/JDT_Core/Null_Analysis)
In the end we need something that has an acceptable license, and can be automatically checked; FindBugs is probably a candidate for that.