See DBD::Pg and the $dbh->func( ... 'putline' ) function. This will allow you to send arbitrary text to the PostgreSQL server.

$dbh->func( q{
    CREATE FUNCTION poo (INTEGER) RETURNS INTEGER AS $func$
    DECLARE
      val ALIAS FOR $1;
    BEGIN
      RETURN val * 2;
    END
  } => 'putline' )
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