You couldn’t do this unless you built custom integrations with each third party - which you said you wanted to avoid.
But you can’t get a third party system to generate something compatible with your own system without building a way for each system to talk to each other.
Rob’s idea would work if you are only doing set promotions - however if you need more variables to calculate cashbacks and promotions and you don’t want to build the front end POS then you’ll have to integrate with third party POS