RTA Guide/Blast Away the Wall

With Full Setup
For the setup, Ledge grab next to plank then press A to get up from ledge grab. Backflip, c-left twice, and press B to punch (make sure you let the punch animation finish before you walk down or he will turn first and it will be less consistent.) Hold down very slightly to slowly walk and ledgegrab. Reset camera by pressing c-right then c-left and hold up to slowly climb up, c-up, then when you see climbing animation, hold straight down.

Plank Push
This is a 100% consistent setup that loses around 2 seconds. It's good to do if you're afraid of missing it in a race, if you ledgegrabbed in a bad spot at first (like in this video) or if you find 2 seconds an acceptable trade-off to get cannonless setup from 95% to 100% consistent in runs.

Video
This strat skips the ledgegrab, backflip and punch of the full setup. The visual cue for the ledgegrab is on the front face of the plank. Mario's left hand lines up with a line in the wood texture.