How to use dynamic flashvars in a block?

Hi!
Thank you very much for this great module!
I want to use flash inside of a block. Because of that, i use the macro [flashnode|nid=12] to show up the SWF-File and it works!
Next step: i want assign flashvars to the SWF. Works like this: [flashnode|nid=12|flashvars=flashvariable=Hello]

And now i want to use dynamic flashvars like this:

<?php 
print '[flashnode|nid=12|flashvars=flashvariable='.arg(1).']';
?>

But it doesn't work!
In the FlashNode i can use

<?php
print 'flashvariable='.arg(1);
?>

and it works.

How can i use PHP and flashnode and flasvars in a block?

Thank you very much for your support!

Tobias