Sorry to ruin the fun but I'm afraid this sale is impossible. Gwern lacks the proprietary rights to his own soul. As the apostle St Paul writes in his letter to the Corinthians (chapter 6), "Or know you not, that your members are the temple of the Holy Ghost, who is in you, whom you have from God; and you are not your own? For you are bought with a great price. Glorify and bear God in your body." It clearly states that "you are not your own" which at least applies to baptized Christians (and as a confirmed Catholic, it may even apply to a higher degree). Unless gwern provides some scriptural basis for this sale, it cannot proceed. Even when Satan tempted Christ, the only proferred exchange was worship in return for temporal power. There are no cases (even hypothetical ones) of a direct sale of one's soul in the Church's Tradition.

In exchange for ruining this sale, I'll pray for your soul for free.