I would restructure the object hierarchy as follows:

package Top::Base;
use Moose; 1;

package SubordinateA; use Moose; extends 'Top::Base'; 1;

package SubordinateB; use Moose; extends 'Top::Base'; 1;
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... and then introduce a new "Top" class that doesn't inherit from Moose and whose ->new method is just a factory for the others:

package Top;

sub new {
    my ($class, %options) = @_;
    my $impl= "Top::$options{ base }";
    $impl->new( %options );
};
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