Back again - Now the right way of doing this was actually just to add the oController: this to the xmlfragment then the event methods get found correctly (which means I can put the CustomTile and class information directly into the XML fragment).
The oController parameter is evident when I debugged the app, but I noticed if you read the description of sap.ui.xmlfragment, it gives you this information, albeit not in the way it does everywhere else in the UI5 API documentation:
https://sapui5.ap1.hana.ondemand.com/sdk/#docs/api/symbols/sap.ui.html#.xmlfragment
Also handy is I can use a completely different view controller for this if I wanted...
Cheers,
Matt