My arrows are 27",too!
There are two possibilities:
Change to a heavy wood like ash or maple( I prefer maple seems to stay straight after sealing);
If you change to heavy woods, please look for quality: My tapered maples are almost indestructable, but straightness of the shaft before sealing is important and straightening must be done using heat. Remember that you will probably have to change your spine number, since maples have a slower dynamic recovery rate. That will usually mean you`ll need heavier spine.
I think it is worth to try Arrow Art for maple arrows. I got a real nice and straight dozen from them!
For aluminums: remove insert and stuff the shaft with a polypropylen rope you can get at a home improvement store in the correct diameters;
adds about 100gr and will not affect spine.