PO25 Markup Individual Lines

Hello - Is there a way to add additional markup's on individual line levels? We have distributors that charge us one markup for cases and an additional amount for lower UOM's. Rather than creating 2 separate headers for those items that have case versus each or box, I wanted to see if I could use PO26.4 for the additional amount on individual lines of the same header. I tested this out by adding 3% on PO25.2 then added 1.5% percent to the line on PO26.4 (for a total of 4.5%), but when I created the PO, only the 3% showed up. Is there a different way to do this? I am on V10. Thank you!