How can I mark a method parameter as @Nullable using an external annotation?

If I browse to a JDK class, and place my cursor on a method parameter then press Alt+Enter, I get prompted to add an external annotation for that method parameter, @Nullable or @NotNull.  However, for a class that is in my code, this doesn't happen.  I can only add external annotations for methods (that have 'return null; in them).  I can add the annotation in the code myself, but I'd rather not do that, as others working on this project do not use IDEA.

Alternatively, if IDEA can do its magic but with FindBugs' annotation names, that might be ok.  Or if FindBugs can do its magic with IDEA's annotation names.

I suppose I can do it directly by editing the XML files in the external annotations directory, but that seems reasonably error-prone and unpleasant.

Any suggestions?