There were sometimes discount codes for Fast-track as well. For an early morning flight it was worth it, one less hassle, I think I once got a free coffee as part of it too.
Interestingly, if you have a booking with Ryanair, you can still add Fasttrack through their website by amending your booking. I haven't done it (yet) but I would be interested to see if it generated the required barcode to proceed through the Fasttrack lane.