Just as an update: I was able to solder up the surface mounted op-amp as per older instructions - ie same pin configurations as ladyada mentioned. Of course it was as little harder due to the smaller pins. But eventually, I think I got it right. To get the wires out from the LCD side, I made two little notches on the upper left and upper right of the PCB from which I let the soldered wires out to the other side. I made the notches to be careful, since I found it hard to get the wires out to the other side since the PCB is flush with the plastic case, and I felt that the wires may break internally or pull the delicate soldering off the op-amp.
Also, I have been able to successfully run the wattcher script too and I get power data as expected, so all is fine. I can confirm that the new surface mounted type op-amp in the new Kill-a-watt design is still usable with the standard Tweet-a-watt design and guidelines. I'll post some more photos of the hookup later.