my @cols = qw(foo bar);
my $sql = <<SQL;
SELECT :foo, :bar FROM dual
SQL

my $sth = $dbh->prepare($sql);

my %hsh;
for (@cols) {
  $sth->bind_param_inout( ":$_" => \$hsh{$_}, 0 );
}

# Set constants...
$hsh{foo} = 'abc';

# Set changing values
$hsh{bar} = 123;
$sth->execute();
while (my @arr = $sth->fetchrow_array) {
  print "@arr\n";
}

$hsh{bar} = 456;
$sth->execute();
while (my @arr = $sth->fetchrow_array) {
  print "@arr\n";
}

$dbh->disconnect();