As you are suppose to know, grass SC is a old tech that Time Trial addicts do using Penta Penguin (because him is faster and have great turns). However, people didn't try it with Coco, and it is so easy! This shortcut is actually just possible on 2nd and 3rd lap, and it saves like 1s per SC (if you do it well). To do this SC, do a mid air powerslide on the downhill to get a good S.G. (speed ghost), and then froggy on the grass. It's simple OpieOP Here is an example of this SC with Coco (two good laps done on CTR token challenge):

Hope I helped you (: