Quite frankly, I don't see why the Entente would ever object to Japan taking over the German concession. Japan already has concessions in China, so what is one more? The UK, France, and the US can't very well complain about Japanese concessions there when each of them also maintain them in China. Besides, Japan is an important power, and one that fought on the Entente side from 1914. Japanese troops shed blood attacking this German territory, they won't want to give it up easilly. China is a weak nation, already sliding into warlordism, that only joined the war late in the game and even then only provided labor assistance. It is far more important to keep Japan happy than it is to keep China happy.
I think Japan might be willing to forgo gains in China if it can get the Racial Equality clause accepted; it would at least be a sop to their pride. But it would be very difficult to get the West (especially the US) to agree to that, even in principle. Alternatively, you could have Japan maintain solely economic rights in Shandong, without military bases and the like (despite the fact that Germany maintained military facilities there). This, after all, is what the Japanese agreed to in the early 1920's. But I think you will run into the same problem: when the KMT begins trying to expand its power, it will go after Shandong. And even if Japan only keeps economic rights there, she will respond with force to protect those rights when threatened.
I can see why so many Chinese were offended at the thought of "losing" territory when they were on the winning side. But China didn't have that territory in 1914, Germany did. Japan fought hard to take it, they won't let it go unless they get something else--something better--in exchange.
(Interesting fact about Shandong: despite the fact that it was only a Japanese concession for 20 years, and despite the widespread anti-Japanese sentiment in China, there are still many Japanese speakers in Shandong today. So much so, in fact, that it is the site of many offshore call centers servicing the Japanese domestic market.)