This had me stumped too, but I looked up the replacement stats at
http://www.espares.co.uk/part/tumbl.../511141/658577/tumble-dryer-thermostat-k.html . There are 3 pictures of the stats, including one from the rear, showing where the hole is.
Once the banjo is off, there are a further 2 screws to remove, which takes the element and the housing for the stats off. You can now access the hole at the rear of the stat. Stick in the pin - job done!
Many thanks to all the posts on this thread - has saved me a fortune & earned me brownie points with wife.