package Thingy;
sub cog_class { 'Thingy::Cog' }
sub get_cog { my $self = shift; $self->cog_class->new(@_) }

package MyThingy;
use base Thingy;
sub cog_class { 'MyThingy::Cog' }

##</code><code>##

package MyThingy::Cog;
sub get_ramp { my $self = shift; $self->thingy->ramp_class->new(@_) }