Ng-model for file input type in embedded form

I found that ng-model won’t work for file type binding. I would like to implement a feature where the approval requestor get back his attached file when his request is returned. I used camForm api to get the file to the scope, but I cannot bind it to a new input. Is there any work around?

I tried this construct:

            <label for="">Attachment</label>
            <div class="controls">
                <a cam-file-download="gm_attach_file"></a>
                <input type="file" cam-variable-name="gm_attach_file" cam-variable-type="File">

but there is error: Form failure: Cannot add variable with name gm_attach_file: already exists.