I suggest sending a lemming over as a climber, and turning him around all the way at the end of the second island. You could probably mine through one of the obstacles.
You can turn them around at will without a blocker?
Have you beaten "Postcard from Lemmingland"? [this level stumped me for a long, long time]. You can use a similar tactic here. There are many ways to turn lemmings around. Most of them involve using a builder.
The most annoying thing about Upside down world imo is the many prickly sticks through the whole level. [not in your picture] They can be a real nuisance. I suggest bashing under them.
That pic btw, is the SegaMasterSystem version I believe, which is quite different in appearance from most other versions. Original the grass is on the bottom.
When you said " that's not actually what I'm talking about." Are you thinking of a different level?