I don't need this in my mod, but just came to my mind that this kind of thing would be really cool, if it's possible to make.
First, make Keen always have the pogo.
Could it be done that when Keen collects that pogo, his x-coordinate would grow with some more, and that could affect as somekind of speed boost. Like for example he would "jump" over 10 pixels.
Then the pogo art could be edited, and place on the ground and so on.. But not to be used too near the walls (that Keen won't go through of them).
That kind of thing could also work as something one-way-teleport-inside-the-level-thingy.
Definitely cool. :)