package Exported;

  # blah blah blah  :)

  our $dbh;
  *dbh = \$main::dbh;

  # now you can refer to just $dbh and it will use the
  # value in $main::dbh
  sub do_query ( $ )
  {
      my ( $key ) = @_;
      return $dbh->selectrow_hashref( ... );
  }