Try doing both. At the same time. (Talk about getting confused while turning....)
Pulling the inside foot back and sliding the outside foot forward at the same time means you are sliding each foot towards the other.
It's almost an impossible task. It feels like trying to move two magnets towards each other, when they are positioned such that they resist coming together.
I've got a name I coined for this. (Laugh if you want....) Magnetension.
Oddly, doing this thing with both feet helps keep the load on the right place under the outside ski so the tail doesn't wash out, and reduces inside tip lead which empowers the inside ski to do its thing more effectively, and makes your feet/skis more stable in relationship to each other. I recommend trying this. If you aren't dyslexic and get it backwards. Which you may, even if not dyslexic.
This is a power source Tesla would adore. Indeed bringing the inside foot back effectively doubles ski input into the terrain so power is effectively doubled. This move does not need to steal force from the main foot, it is loaded and working, magnetension brings the smart brother into play leading the way to the next turn. This slight pressure on the boot front wakes up the tip and I swear I can feel the radius decrease to match the outside ski, maybe that is my imagination, but it does provide a badass way to shape the turn.
Many an instructor belittled the idea as blasphemy on the ski lift as I babbled on about it like some madman, MANGETENSION! The second law of thermodynamics work in in a closed set, skiing is dynamic.
I tell this to folk who need to use both skis, one ski skiing can only take you so far.