Able to create a custom roadmap containing initiatives from each level of a 3 tiered product hierarchy

Given that I have a 3 tiered product hierarchy (Grandparent Product Line > Parent Product Line > Child Product)

And I have initiatives at the product level which roll up to initiatives at the Parent Level, which roll up to initiatives at the Grandparent level,

I would like to be able to create a road map of the Child Product Initiatives, filtered by the Grandparent Product Line Initiatives.

This would provide much needed granularity on strategic roadmaps. Our key strategic initiatives are found at the Grandparent level, and often the initiatives at the Parent level do not provide enough detail. Therefore, I'd like to be able to create a roadmap with product initiatives filtered by Grandparent initiatives.

Currently the "Initiative Roll Up" option does not allow this, as it only caters for a 2 tier product hierarchy. The only workaround is the "Hierarchy" report, but this does not provide the nice visual of a roadmap.