I do exactly what forum member 153957 describes above. I use and recommend Hugin.
To add to 153957's description --
. I label all panorama or HDR sets with a yellow label, in addition to staking them. This keeps me from accidentally adjusting, moving, or deleting them.
. After import, I make the stitched photo the Stack Pick.
While it will help keep things simple to use Aperture as much as possible, there is no reason to avoid using other, better, tools as needed. And you should realize that plug-ins are external programs which simply automate the creation of a file to be exported, its export, and the importation of the edited file.
I don't know of a stitching plug-in. Nik has a new HDR plug-in which has garnered positive reviews.