Ended up using the wrapper script approach:
Not pretty, but it seems to work.
Code:
#!/bin/bash
NVIDIA_DISPLAY=":1"
trap 'kill -TERM $PID || true' SIGINT SIGTERM SIGHUP
/usr/games/dolphin-emu "$@" &
PID=$!
nvidia-settings -a '[gpu:0]/GPUPowerMizerMode=1' -c $NVIDIA_DISPLAY 2&>1 > /dev/null
wait $PID
wait $PID
nvidia-settings -a '[gpu:0]/GPUPowerMizerMode=2' -c $NVIDIA_DISPLAY 2&>1 > /dev/null
Not pretty, but it seems to work.