While there is nothing in the rules that says you can't, I can't think of any reason why you would want to do such a thing. I guarantee you that driving down the ramps is a better route to take in every possible way. It would be faster, safer and all together better for your team for you to drive down. With that being said...to try what you are suggesting boarders on 'not racing' in the same way that climbing the ropes on Gephy would. There are no written rules that say you can't climb the ropes either but you would have to stop racing to do it. I would look at your scenario the same way and suggest that you not try it. It only takes a little practice to become competent enough at driving the ramps to make that a far better choice.