I have a shop where some of my customers get a 30% wholesale discount on some of the products.

I can set up 7.x-3.0-alpha0 so that it applies a wholesale discount line item to the order. That works well enough, but it makes a mess out of accounting. There's no simple way to tell what products were purchased at what price.

I request an option such that the sell price of each applicable product in the cart/order is modified to reflect the discount, with no separate line item.

As a sub-option, the coupon can appear (or not) on the cart/checkout, but just as a sign that the discount has been applied.