Thank you, Olaf & Scott, both comments were really helpful!
I've downgraded Olaf's answer from "Correct" to "Helpful", hoping this increases the chance to found anyone else, who has tried already something more.
I'm still hoping, there is a (maybe secret) simple way to "enable more SNMP" on this devices.
Submitting an idea for using the netifTable could be successfully, of course.
But I afraid, it will take a long time to get enough votes for this very special theme. So, this will be "plan B".