First let me ask you: has he actually been tested to determine that he is HSV 2 negative or does he just think he does not have herpes. If he has not been tested, that should be done.
Because people who have buttocks lesions also shed from the vagina, I don’t believe that any one sexual position is more or less risky than any other position.
He could get the virus from giving you oral sex but that is not common at all. If he did get it orally, he would basically be vaccinated against getting it genitally and it would look like a cold sore on his lip .
If you do not have an outbreak on your buttocks, spooning is absolutely fine. With an outbreak, I might suggest jammies.
Please let me know if you have other questions.