Just thought I'd point out to you guys that this thread is over 4 years old, and the OP has been inactive for over 3 years.
Who cares. I am very interested in this topic. Here is a sim I did of the circuits Einar posted. I hadn't encountered these before.
Note that they transform the effective resistance of R3 as claimed.
This will not of itself help to transform the resistance of a gas-gauge sender because these two circuits require that neither end of R3 is grounded. Note the voltage plots V(b) and V(c) for the two circuits and the Plots of V(b)/I(I1) = to input resistance at Node b. The example Divide circuit cuts R3 in half while the Multiply circuit doubles R3.