They could hold up Dorian and ask Satoshi to post something requiring his key, although that couldn't discard the possibility of Dorian having instructed an acquaintance to do so in case of emergency.
There's really no way to prove (a posteriori) without doubt that someone is or isn't Satoshi, unless there was an encypted message left by him (a priori) saying "My DNA is (...)", to which he provides the key.
There's really no way to prove (a posteriori) without doubt that someone is or isn't Satoshi, unless there was an encypted message left by him (a priori) saying "My DNA is (...)", to which he provides the key.