Super Orders 2.0 postage marks with Super Orders

I've just installed the super orders 2 module which is excellent! What I have a combined invoice and label template. I can get the system to print out the info in the correct places no problem but I was wondering how I would go about getting the system to choose the correct postage mark based on what the customer chose while ordering?

The customer has 2 options when ordering 1st class or 2nd class.
I need the system to put the first class postmark on the label if the customer chose this one and the 2nd if that was the one that was chosen. I have both postage marks as .jpg images which I can upload to the site.

Can someone please tell me how I would set the page up to select the correct one? :unsure: