You could try clamping fuel resistant fuel line around the inner pump. It is available in a few different diameters, cut three pieces that can go around the inner pump, split the hose and secure with stainless steel cable ties. Or cut the hose about 1" short of the diameter thread stainless ties through the hose and tighten in the gap. You will need to stagger the joins at 120 deg. Once you have the hose secure on the inner pump push it into the old shell.
Regards Martin.