So, I ran a test where I defined 5 instances of the 18B20 driver on 5 different pins, 2,4,5,12,13. Then I modified the temp command to take an additional pin number argument, so for example, while I had the oled still hooked up to I2C on pin 2 & 3, I ran:
temp 0 2 curr
(which means read sensor 0 on pin number 2)
which reported -196 degrees (since the 18B20 was still on pin 5, but the oled still worked!
Then I disconnected the oled from pin 2 and hooked the 18B20 to pin2, and it immediately started to read the temperature!
So, we may be able to define i2c on other pairs of pins as well, and as long as you don't try to perform I2c and onewire ops on the same pin in your program, it just may work fine in practice.