Reporting Marketing Influence on Existing Customers

[Anonymous]

I know an earlier discussion many years ago that touched on the topics of reporting on marketing impact for cross sell/upsells: 
https://community.marketo.com/MarketoDiscussionDetail?id=90650000000PTriAAG

We are thinking about using attribution to specific upsell campaigns or interactions within x time frame before an upsell opportunity is created, however we feel both methods wont quite capture what we are  looking for. I wanted to see if there are any new creative ways in measuring marketing influence for existing accounts that anyone would like to share since the last discussion. 

[Josh_Hill13]

What would you like to do exactly? What about the other methods won't work?

[Anonymous]

Ideally we would like to track activity any leads attached to upsell opportunities that have interacted with our campaigns after the close date of the original new business opportunity (when they became a customer). 

Is there a method of dynamically capturing ROI and campaign influence based off individual opportunity close dates rather than a static time period?