I am implementing digital voltage and current measurement on an old power supply.

Due to the design of the supply, I am forced to use the positive output probe as a common ground for my ADC and MCU.

However, this means that both the voltages on R1 (0 to 0,5V) and R2 (0 to 5V) will be negative (as measured by V2 and V3) in reference to ADC and MCU, which I need to convert to positive for ADC measurement.  

I cannot use op amp inverter, because load resistance will be variable, which makes fixed unity gain impossible.

I don't really have any other ideas.

What would you do in my place?

I am implementing digital voltage and current measurement on an old power supply.

Due to the design of the supply, I am forced to use the positive output probe as a common ground for my ADC and MCU.

However, this means that both the voltages on R1 (0 to 0.5 V) and R2 (0 to 5 V) will be negative (as measured by V2 and V3) in reference to ADC and MCU, which I need to convert to positive for ADC measurement. 

I can't use an op-amp inverter, because load resistance will be variable, which makes fixed unity gain impossible.

I don't really have any other ideas.

What would you do in my place?