I don't see any problem using orange in addition to the hops. You should probably just use zest, though, not the whole peel. You can add it at or near flameout easily--just grate a whole orange into the wort. Even an entire orange will add a subtle flavor. You could also consider adding up to an ounce of ground Indian coriander, which has a bright citrus aroma.
On that note, if it were my beer, I think I would use something other than Sorachi Ace to combine with the citrus. Of course, you have experience with that hop yourself, so you already have tried it and liked it. But to me, it doesn't taste all that much like lemon; it tastes much more like dill. So again, if it were me--but it's up to you--I would add something more "citrusy," such as Amarillo, Cascade, or Summit. Another choice would be Motueka, a New Zealand variety, that to me has a clearer lemon taste.