Variable Directory Issue Using cffileupload

Can anyone help with how to set a variable directory in cffile when using cffileupload? Here's my simplified code:

<!--- APPLICATION.CFM --->

<cfapplication
    name="test"
    sessionmanagement="yes"
    sessiontimeout="#CreateTimeSpan(0, 0, 20, 0)#">

<!--- UPLOAD.CFM --->

<!--- Simulate Session.clientId as if client has logged in by setting it here --->
<cfset Session.clientId = "1" />

<cffileupload url="upload_action.cfm" />

<!--- UPLOAD_ACTION.CFM --->

<!--- this works --->
<cffile
    action="uploadAll"
    destination="#ExpandPath('./upload/1')#"
    nameconflict="makeunique" />

<!--- this does not work --->
<cffile
    action="uploadAll"
    destination="#ExpandPath('./upload/#Session.clientId#')#"
    nameconflict="makeunique" />

<!--- Note. Directory structure ./upload/1 exists --->