Fun with Streams

I created a stream wrapper around the php_writeexcel library found at
http://www.bettina-attack.de/jonny/view.php/projects/php_writeexcel/

My code can be seen at http://www.pastebin.com/m7212eaa2

I'm trying to add an option that will allow us to lower or uppercase
the column headers we create by calling ftell on the Excel stream but
when I do something like...

   $xls = fopen("xlsfile://../data/measurables.xls","wb"); echo ftell($xls);

...I get 0 returned even though I've hard coded a return of 123 in my
stream_tell function (which I did to see if my stream_tell was even
being called).

Can anyone tell me what I'm doing wrong or suggest another way to
"communicate" into the stream wrapper that will be compatible with PHP
4 and 5 on OSX, Linux and Windows?

Thanks

Matt