I recently obtained the wiring diagrams for the 2012 Yaris. Much of the wiring and connectors remain the same as the second generation Yaris. This is the case for cruise control, so 2012 Yaris owners can DIY cruise control using the same OEM stalk.
For the 2012 the wiring is the same as that of the 2009-2011 Yaris, where the wiring from the ECM to the steering column is (theoretically) there. Also, the 2012 Yaris has the cruise control "On" and "Set" indicators built into the instrument cluster.
For those with the steering wheel audio controls the spiral cable connector, under the airbag, is a 10 pin connector, instead of a 4 pin connector (like those without steering audio controls and that of the 2006-2011 Yaris).
Attachment 44502
Those with the audio controls will need to transfer the two cruise control pins (in positions 1 and 2) from the 4 pin cruise control stalk wire to their 10 pin spiral cable connector (in positions 1 and 2).
The procedure for removing the steering wheel airbag is a little different for the 2012, where three clips secure the airbag to the steering wheel (rather than 2 screws like the 2006-2011 Yaris).
Attachment 44503
Also, for the 2012, the lower steering wheel cover has a separate removable cover section for where the cruise stalk goes through, called the "lower no. 2 steering wheel cover"
Attachment 44504
If someone from the Connecticut area is interested in adding cruise control to their 2012 Yaris, I have the parts and would be more than willing to help to give me the opportunity to document the process and update my Cruise Control DIY.