Aggregating build artifacts of dynamically created builds

I have a build configuration, say RunSuites, which is parameterized by the suites to be run. I have another build configuration ParallelRunner that runs, say, 2 builds of RunSuites with different parameter values. It does this via the REST API. I'd like to aggregate the results of the 2 builds of RunSuites. ParalleRunner may spawn 1 or 2 or 3 or N builds of RunSuites.  It's not possible to create unparameterized build configurations for all possible parameter values. 

How do I do this?

I've seen the Composite Build Configuration. That allows one to specify that one build *configuration* aggregates multiple other *configurations*.