thank you very much for your answer.
Frankly, something really hilarious just happened! Based on your answer I wanted to comment that I believe this functionality should be built into the "aggregate" functionality. I wanted to use the correct terminology, so I looked up the operator in RapidMiner, and - shame on me - I actually figured that it is already there, itīs the aggregation function "concatenation
Thatīs precisely what I was looking for, and SO simple!
Again Andrew, I do thank you for your answer, after all you pointed me in the right direction, and you also gave me a glimpse of a more flexible approach. (Not that I could do that (yet), but down the road... who knows?