Webaction : evaluating the filename argument of clp_include clp function

Hello,
Can someone help me in this WebAction problem: 
In a Webaction clp page I'm using 
<clp_include name="filename"/>
But the file name I want to use is stored in a web session variable
(websession-variable (websession-from-req req) "file-name")

If I use <clp_include name=<clp_value name="file-name" session/>/>
It doesn't work

Thanks
Jacques