I put a lot in the title to make this post easily searchable by all inquiring posterity. Anyway, the libnetNet::FTP module API has a retr() method that returns a Net::FTP::I object and that class has a read() and write() method. But I did not see a seek() method.

However, the docs for Net::FTP do state that all normal I/O methods can be applied to Net::FTP::dataconn objects and Net::FTP::I does inherit from this class, and even further up the hierarchy is IO::Socket::Inet and even IO::Handle, so logically it should work. But none of these manpages document a seek() method, so I don't feel that partial content is possible using Net::FTP, but I would be overjoyed to be proven wrong.