SAC Analytics Cloud - aggregation

I need to graph an average of cumulative data, based on a transformed date dimension* with a live connection.

*We modified the date to a number to allow comparison between the Nth workday of the month, eliminating differences in holidays and different starting days in the month.

So the above should be this (of which i need to display the last column in a line graph with the number as the x-axis):

I have already seen several articles/resources offering different possibilities, but none of these solutions have worked for us (among others; https://www.linkedin.com/pulse/4-ways-calculate-accumulative-sum-sap-analytics-cloud-t%C4%83lmaciu/).

Since i can't change the datasource I thought I could simulate solution 4 of the article by adding a seperate excel file to transform the number to a cumulative, and link the dimension.

so this:

But i can't seem to get this to work either.

Does anyone how I have to do this (or if it is possible at all)?