A quick an dirty workaround would be to have an NPC where you can get ascended select-stat copies of your legendaries. Make them soulbound, unsalvagable and unsellable like some of the old personal story rewards. This could also be implemented without an NPC with an option like "withdraw duplicate" in the right click menu of a legendary. If you want to use this totally optional system you have to sacrifice inventory space for added utility.
Yeah, its basically the same as just using ascended from the beginning - but it kinda imitates the stat swap mechanic of legendaries.