You could use a stout leather lace, tied in a slip-knot looped around the headstock under the strings just past the nut, with only one strand of said lace connecting to your strap. Position the knot so it's not in your way and the lace can be a few inches long so the single strand is the only thing that might interfere at that end. I used to strap on my mandolin this way; actually, the whole strap was just a stout leather lace. But I've since attached a strap button to the body just above the heel. It's a polymer-backed mando by Ovation with access through the back to the inside so it was easy to reinforce the attachment point.

Attaching it to a button too far out on the headstock would apply a lot more more torque to the neck, I'd think. The debate rages on about whether that's a problem of course, but I prefer a strap connection closer to the body, especially on a guitar.