Thanks Jamie,
The idea of subreports with their own grouping is just great! I never thought about it.
Crosstab is also a good suggestion.
Neither of them would probably work in this case because Details subsections in this report are heterogenic: there are subsections with subreports and there are sections containing fields/formulas from the main report. Even in the picture I posted there are two subreports jammed between other subsections.
In any case I really appreciate your input. I am sure I will have a case before long where your suggestions will work wonders!