$value =~ s/\./->/g;
...
my $generator = eval "sub { $value }";
die if $@;

for (@rows) {
    ...
    print $generator->();
    ...
}

##</code><code>##

# untested, just pseudo code

my @tokens;
local $_ = $value;

while ( !/\G$/gc ) { # while not at end of string
   push @tokens, 
     /\G\./gc ? [ 'DOT', '.' ] :
     /\G(\$\w+)/gc ? [ 'VAR', $1 ] :
     /\G(\w+)\((.*?)\)/gc ? [ 'METHOD', $1, [ split /\s*,\s*/, $2 ] :
     /\G(\w+)/gc ? [ 'METHOD', $1, [] ] :
     ...
     last
}

##</code><code>##

# again, untested, just for demonstration

my $code = '';
for (@tokens) {
   my ($type, $source, @params) = @$_;
   if ($type eq 'VAR') {
       $code .= $source;
   }
   elsif ($type eq 'DOT') {
       $code .= '->';
   }
   elsif ($type eq 'METHOD') {
   ....
}

my $generator = eval "sub { $code }";
die if $@;

for (@rows) {
   ...
   print $generator->();
   ...
}

##</code><code>##

my $generator = eval "sub { my (\$order, \$order_line) = @_; $code }";
...
$generator->($row->{order}, $row->{order_line});