Coupon promotion - Added to all line items

Hello - We're using coupon promotion. We've modeled it in such a way that it does NOT appear as separate line item in the Quote ( "Show in Catalog" is unchecked). We've added all products in this promotion.

The issue is when I select promotion on 1 line item, Siebel automatically updates other line items with the same promotions.

Our requirement is to let use select promotion for each item

How can we achieve this requirement?

Thanks