you definitely can, try again
ps : with what device are you playing ? (keyboard/gamepad)
I tried with keyboard, d-pad, and analog stick. Always the same result. Whether I hold down-left and press the morph button or if I hold morph for a little bit then try to move, whether I'm pressed against the corner to start or if I jump and try to line up diagonally with the gap, the sprite just jiggles a lot and nothing happens. I tried for about 10 minutes and I couldn't get it to work.