I've spliced quite a few of my aluminums. Usually I splice them with a smaller diameter shaft about 4" long inside, which puts 2” on each side of the splice. At a minimum, the short side of the splice needs to be 2” plus the depth of an insert.
This works for me, as I shoot 32” arrows and my spliced shafts are typically either flu-flu’s or stumpers. Aside from going the cut them shorter route, you’d probably need to find/make a longer insert to just add ½”. Good Luck…Enjoy, Rick.