Woo commerce

I have a woocommerce shopping cart and I'd like to offer visitors 30% off any product if they come via ppc of google display network campaign. If they don't, I don't want to make the offer. Looking for someone who is very familiar with woocommerce that has 'Solved' for this problem before. I need the solution in place in the next 4 hours. I will do the work, just need step by step directions.