Thoughts on Challenge due to Significant Concavity in Implant Site?

This patient desires implants in #3,4,5 sites. #5 was recently extracted with graft placed at #5 site. My concern is the amount and location of quality bone. From the axial view you can see the #5 site has a significant concavity. From a restorative perspective, the crown would be placed outside of the normal arch form. Vertically there is minimal space, perhaps 6 to 10 mm for placing implants. I have done several cases similar to this, but there was slightly more bone and it worked out fantastically. What would you recommend? Horizontal ridge expansion? Sinus lift? Patient would rather not have additional bone grafting, but she says she will do whatever I recommend.