No need to change microcontroller. The 12F683 has 256 bytes of EEPROM in which you can store whatever you want. Use the WRITE and READ commands to store and retrieve your values.
How to implement it depends on how often the value changes. The EEPROM has an finite number of write cycles so if the value changed several times per second it's not a good idea to constantly write it to the EEPROM, in that case you need som power fail signal which triggers a write. If the value doesn't change very often a simple timer which triggers a write after 5 seconds (or whatever) of unchanged value should be good enough.

/Henrik.