Create a 3D curve and attach the interior edges. Also, use transfinite interpolation (tfi) which spreads the perturbation smoothly across two regions. You have to inspect the region with the greatest distortion, then determine how to change one or more of its boundary edges to improve it without cause of serious degrading of the neighboring regions.
In regions where the aspect ratio is bad, use res or one of the other nodal distribution commands along one edge to improve the aspect ratio in one area at the expense of a poorer aspect ratio or element quality in the neighboring regions.
