Yes, you can use DBI directly by getting the database handle. This can be done by calling class->db_Main(). You can use it exactly like you would use regular DBI.

sub foo
{
  my $class = shift;
  my $dbh   = $class->db_Main();
  my $sth   = $dbh->prepare_cached("SELECT ...");

  $sth->execute(...);
  #... usual DBI stuff
}
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If you then want your return to be objects from the data you retrieved, you may want to look into sth_to_objects() or construct() methods.