groundfungus:
I just dealt with this same problem. I ended up using the liquid crystal library. In setup use LCD.begin(16,2);. Then when you want to write to the right 8 character's, use LCD.set cursor(0,1) then LCD.print() (or LCD.write).
Isn't that essentially what he is already doing in his original program?
The library really doesn't do much with the first parameter in lcd.begin(x,x) - it is the second parameter that you must match with the number of lines of controller memory that you are using. This would 1 for the few true 16x1s that exist and 2 for all the others.
Don