conservative and non-conservative extrapolation and appropriate usage
Based on the density altitude calculations we were required to learn for PPL, my approach would be to use a higher altitude/lower temperature giving the same density altitude and enter the chart that way.
That appears to be conservative because engine power reduces faster with altitude than with temperature, so higher altitude/lower temperature should give a longer distance.
However, given the short distances in the chart I probably wouldn't take off if the runway available wasn't significantly greater than what was calculated.