cesisco: Thanks for the link! I saw your example long ago and thought it was cool, but it kept crashing if I move it too fast.
Thanks for the help everyone. After quite some time of researching, this is the version I am going for, as it's easiest for me to understand and implement, without going to UID picking and looping.
Here's the capx, for those interested. It's not perfect, but it's good enough for me.
If any of the expert has a better and proper way to implement this, please do share.