I think a solution would be as follows: in the upload forms, set the following configuration: <*var_uploader_id>:VAR(USER_ID).OR(None);<*/var_uploader_id> and
<*var_uploader_name>:VAR(USER_NAME).OR(Guest);<*/var_uploader_name>.
With this, you can use the variables to display the name and ID of the user who uploaded, instead of using %username% and %userid%.
PS: Remove the stars (*).

Not fair whithot check