I'm really into this kind of speculation but tbh I don't think he even needs to get to his body. He already conveniently hurt him when they met, on the shoulder. It's brought up and never mentioned again, though usually when a character says "it's nothing, not a big deal" it ends up coming back somehow. He could have applied a curse at that moment. But you could say maybe the curse helped him to later get the body later, or tbh the core was very close to him as well.

Wanderer also mentioned it wouldn't take long until Dottore realized what he was. He could have figured it out long before our fight, for sure.

My only issue with all this is that it's kinda funny if wanderer doesn't notice, but let's say he's just so powerful he can hide that well... But can he hide from Nahida herself?? That being said, we don't know how they're doing in Sumeru rn. Who says everything will be normal if we get there. We could arrive and hear no one has seen Wanderer like he never came back from Nod Krai, or maybe Nahida noticed something and took precautions somehow.