Survey after Hangup

No need to use the override context, extensions_custom should work

Do you have the queues pro module? If yes, then create a custom destination pointing to macro-survey,s,1 then make the post callee destination the custom destination.

https://wiki.freepbx.org/display/FPG/Custom+Destinations+Module

https://wiki.freepbx.org/display/FPG/VQ+Plus+Options+in+Queues#VQPlusOptionsinQueues-PostHangupDestinations

Another option is to use something in here to trigger the event.

Lastly, if you need something more simple, can you have the agent transfer the caller manually?