Can I reach this place in Superfrog?
I'm going to go out on a ledge and assert that no, you cannot. I'm basing this opinion on this longplay, which shows the area in question at 1:39:39.
The author of that video goes to great lengths to show all the hidden passages, item collects, etc, and seems to indicate, through jumping around the pencil that it is impassable.
It's not proof, but barring the game's developer making a statement to the contrary I don't think we're likely to get any further on this one.