Use JB Weld to install a brass insert and you will have no weakness in the shaft for the full length of the insert. Adding any additional external material that is shorter than the insert length will only add weight and diameter. Being that the shaft will be bonded to the full length of the brass insert resulting in a single unit, I doubt you will see any strength issues within that length.
Any footing added for the purpose of increased strength and reduced breakage would need to extend beyond the insert length. Externally the best option is a length of 2413 arrow shafting that is epoxied into place, but this does increase the external diameter of the shafting. I prefer an internal tapered footing which not only eliminates the increased diameter, but it also eliminates having an abrupt transition at the rear of the footing. Many times by adding a stiff external foot with an abrupt transition, you are only moving the weak spot directly behind the head/insert further back on the shaft without eliminating the weak spot:)
Best,
DB