Then I guess I have to tweak XML::Simple :-)
Here is a patch that adds another option for suppressempty that instructs XML::Simple to keep the whitespace IFF there are no subtags.

--- XML/Simple.pm~    Tue Oct 22 20:05:02 2002
+++ XML/Simple.pm    Wed May 19 16:22:56 2004
@@ -690,6 +690,7 @@

   # Add any nested elements

+  my $keepspaces = (scalar(@_) == 2 and $self->{opt}->{suppressempty}
+ eq '0'); # only if there are no subtags
   my($key, $val);
   while(@_) {
     $key = shift;
@@ -700,7 +701,7 @@
       next if(!defined($val)  and  $self->{opt}->{suppressempty});
     }
     elsif($key eq '0') {
-      next if($val =~ m{^\s*$}s);  # Skip all whitespace content
+      next if (!$keepspaces and $val =~ m{^\s*$}s);  # Skip all white
+space content,
       if(!%$attr  and  !@_) {      # Short circuit text in tag with n
+o attr
         return($self->{opt}->{forcecontent} ?
            { $self->{opt}->{contentkey} => $val } : $val
@@ -1426,7 +1427,7 @@

 When used with C<XMLin()>, any attributes in the XML will be ignored.

-=item suppressempty => 1 | '' | undef (B<in>)
+=item suppressempty => 1 | '' | undef | 0 (B<in>)

 This option controls what C<XMLin()> should do with empty elements (n
+o
 attributes and no content).  The default behaviour is to represent th
+em as
@@ -1433,8 +1434,10 @@
 empty hashes.  Setting this option to a true value (eg: 1) will cause
+ empty
 elements to be skipped altogether.  Setting the option to 'undef' or 
+the empty
 string will cause empty elements to be represented as the undefined v
+alue or
-the empty string respectively.  The latter two alternatives are a lit
+tle
-easier to test for in your code than a hash with no keys.
+the empty string respectively.  The latter two alternatives are a lit
+tle easier
+to test for in your code than a hash with no keys.  Setting the optio
+n to 0
+will cause elements containing only whitespace to stay intact in the 
+resulting
+structure.

 =item cache => [ cache scheme(s) ] (B<in>)
[download]

That is if you set suppressempty=>0 then

<tag>  </tag>
[download]

will produce

$data = {
 tag => ' ',
}
[download]

, while

<tag>
  <subtag>hello</subtag>
  <other>world</other>
</tag>
<code>
will produce
<code>
$data = {
 tag => {
  subtag => 'hello',
  other => 'world',
 }
}
[download]

I'll submit the patch to Grant McLean in a few days if there are no problems with it.

Edit by castaway: Closed small tag in signature