Does what the single man did, by concluding a contract of "I marry myself to you," then engaging in sexual intercourse and divorcing two days later, count as a circumvention of zina (unlawful sexual intercourse), and does he incur sin for it, Islamically speaking?

What transpired between the man and the woman is considered adultery (zina), and there is no validity to the man's statement to the woman: "Marry yourself to me," because this is not a legitimate marriage. It is a manipulation of the Sharia and an audacious transgression of God's boundaries. The man must repent to God for this abomination and for his manipulation of the Sharia rulings, and he must avoid the causes leading to adultery, such as free mixing and unlawful seclusion. He should also emigrate from disbelieving lands if he cannot preserve his religion therein.