It's great that you're planning to undertake such a task - that requires years of dedication, motivation, and hard work! Even as a native Chinese speaker, I believe that Chinese is an extremely difficult language to learn, and I think the Ivies would definitely look favorably upon this. You could try to prove your proficiency by taking the SAT II subject test in Chinese at some point, or even the AP test if you're ambitious enough.
Otherwise, there are also the HSK (Hanyu Shuiping Kaoshi) diplomas that are developed in Beijing and recognized throughout the Chinese speaking world. Keep in mind that the latter is really difficult though - a 5 on the AP Chinese exam would only be equivalent to a Level 3 HSK Diploma, and there are 11 levels in total. Just something to think about if you really want to pursue your Chinese studies in-depth.