Feature Request: Applying Discounts to Items On Checkout Rather than Automatically

[#1]

Problem

We are a salon that creates promotions. For example, we may run a happy hour special for a slow week and offer 25% off color services for our Level 1 and Level 2 stylists (we have 4 Levels). Or we may offer 25% off a conditioning treatment on Mondays & Tuesdays. The current discount trigger that applies to certain services or products can only be applied automatically and without constraints to the provider level or specific dates. The other option is to create a 25% discount that is applied manually at the time of checkout, but it will only apply to the entire ticket, which does not work if someone buys a product or adds a haircut to the discounted services. We offer discounts to get people in and then be able to upsell them. We don't want to discount our upsells. 

How Might We

How might we create discount triggers that fire manually at checkout and only apply to certain items or services that show up on the ticket but not the whole ticket?