This is discussed in section 6.2.5 ("Implementing abstract methods") of TheDamian's classic book, Object Oriented Perl. The technique he outlines is simply to define the method normally and ensure its code throws a suitable exception. If it gets too tedious to do this manually, he presents a utility method to do it.

Given the number of questions you ask and your obvious love of Perl, I'm sure you'll get many hours of enjoyment from this wonderful book. ;-) And it has an excellent appendix comparing Perl with Java (and C++, Smalltalk, and Eiffel) feature-by-feature.