Did I loose some notes? Basically, use a Vcc -> R -> diode followed by a buffer as REF voltage for a DAC. Send DAC output to a summing amp with 1R coming from REF and 2R coming from DAC. Summing gain set to 1/3 DAC, 2/3 DC (e.g. just a buffer). This should give ballpark voltage levels. As long as OSC/CONTROL transistors are thermally coupled, digital comp can be used to calibrate the pair.