I blogged about OBIEE and Dual Y line chart: OBIEE- Narrative and dual Y axis Google Chart
Yes, I blogged about OBIEE and Dual Y line / bar chart: OBIEE - dual Y bar using BI Publisher
It seems there is much easier, but not supported and not recommended way.
Create a Report with dual line bar chart:
Change “bar” to “line”. Press Apply XML.
Everything seems to keep working fine:
You prefer dual axis Y bars? It’s on the house. Same solution, just change "line" to "bar".
Everything is fine if you don’t touch the measures in the bar or line part in the chart editor.
You did? You return to the Line / Bar chart.
Advantages: Built in, integrated, Printing works fine.
Disadvantages: Not supported, it might stop working after an upgrade in the future. To the best of my knowledge; Each time you interfere in the XML, Oracle is not responsible for the results.