CREO 13 Sheet metal DXF export: include thickness in filename

I’m using the new flat pattern dxf export feature in CREO 13 and so far it is working very good.

However to further automate my workflow, I would love to include the thickness and possibly the material in the filename.

In the export dialog, I tried setting the file name to:

&model_name_&smt_thickness

but that gives an illegal characters error.

Is there any way to do this?

Additionally it would be convenient to export any parameter as text like you can export width and length currently.