Net::FTP supports a BlockSize setting that might have an effect if set very low. But I think that's doubtful.

I think my first try would be to call get with a filehandle as my local file (get supports either a file name or a filehandle). You could then presumably tie the filehandle to a homegrown object that implements a WRITE method that limits bandwidth by going to sleep periodically or something. Completely untried, but that would be fun to give a shot ...