SAP Analytics Cloud: Blending two models using Live Connection to show remaining value

Hello SAP experts,

Im struggling with blending two models in the live connection from BW, and I hope you can help me:

I need project remaining amount of maturity as a line within the another model using BW Live connection.

I have a date on X axis and paid amount of maturity each period on Y. Each year is the amount paid and the value is being drawed from the total sum each time. This is represented by the red line. My proposition is to make two models, one with amount paid each year and the second with remaining maturity value and i need to merge it to be able show the graph underneath. How it can be done?

Or is there an option to calculate values directly in live connected BW datasource in SAC, so the calculated measure can show remaining value?

Thanks in advance!

Milos