There should be an option within the Sweep modifier to place a custom shape such that it's pivot is where it rises on the base spline.
at the moment, we only have options for the 8 extremes and it's geometric center, and while an offset will have the same net result, the fact that the offset needs to added manually, just to get it to consider the origin again is... inconvenient.
Can't find what you're looking for? Ask the community or share your knowledge.