Alas, no. "Auto" is a Percentage of Current size, or you set it manually -- no more.
But still I find it a little strange that Adobe has the auto leading set by percent. Changing a font size from 25 to 75 with the auto leading will make the leading to big. I might be wrong but I thougt the leading size is based on some recomendations, like a value betweed 1 to 3 points over the font size, no matter how little or big the font is.
I guess I have a new feature request :-)
Basically one can say regular text is less then 18 pt size.
So, especially with small sizes, setting auto leading to "size + x pt" would lead most often to wrong views: 5/7; 6/8; 9/11. Percentage is more suitable in this case, I guess.
If you think leading should be 2 pts larger than font size you ALWAYS have the opportunity to set it that way in your paragraph style. Auto-leading is a convenience, but not a requirement, and for headings it is totally inappropriate.