as there are no rear speakers or wires to the rear of the car is it possible to splice the front speaker wires and attach more to run to the back of the car?

you have rear speakers. and no i would not splice in to the front . you could blow the radio and a new radio from toyota is $431.51 THE LOWEST $1183.75 the highest.

Toyota shows all models as having rear speakers. The 3 dr hatchback has them in the rear quarter panels The 5 dr hatchback has them inthe rear doors. The 4 dr sedan has them in the rear doors also.
Hope this helps! God Bless!