aarg:
Why would a simple voltage divider not work?
It could possibly work. The main problem is that the description of the system isn't clear at all.
So far, we know there's a sensor that outputs some voltage between 0 and 5 volt, and this output voltage appears on a line (with respect to a ground). And the OP reckons he/she wants to change a 'voltage' dynamically. It's unclear 'which voltage' or 'what voltage' needs to be changed dynamically.....eg....the sensor's output voltage?
Or some other voltage along the line that could be sniffed with a big potentiometer that doesn't load the line down too much.