I don't think this will be extremely helpful because it doesn't answer your question directly, but maybe it will provide some clues. I am running the 3.0-stable release which is Ubuntu 18.04.1 and CUDA V9.2.148 by default. The interesting part is that it also has CUDA 8 installed. So, I started looking into how it supports CUDA 8 by toggling back to it. I started by grepping for cuda in the mining directory. There were two hits of interest - 0miner and screenrc-miner-cuda-8. So in screenrc-miner-cuda-8, we have these env var changes to toggle back to 8:
## set cuda-8.0 env for older miners
setenv PATH /usr/local/cuda-8.0:$PATH
setenv LD_LIBRARY_PATH /usr/local/cuda-8.0/lib64:$LD_LIBRARY_PATH
And this screenrc is called by 0miner with this code:
# List of cuda-8.0 miners
CUDA_8_MINERS="ANXccminer ASccminer KXccminer MSFTccminer NAccminer SILENTminer SPccminer SUPRminer VERTMINER"
LAUNCH="screen -c ${NVOC}/screenrc-miner -dmSL miner"
for miner in $CUDA_8_MINERS
do
if [[ ${!xminer} =~ $miner ]]; then
LAUNCH="screen -c ${NVOC}/screenrc-miner-cuda-8 -dmSL miner"
fi
done
So, if the coin you chose has a miner that requires CUDA 8, then it toggles $LAUNCH to use a different screenrc which in turn handles the necessary env var tweaks.
Hope this helps.