If you knew where the weak/strong side was you could refletch accordingly to at least make them all flex to the weak or strong sideand should see an increase in accuracy. But how do you find the weak/strong side?
If you do not have access to a spine tester, there is another way, but it is done by feel. Get three roller bearing that will fit over the shaft with a little bit of friction. Put one on each end and one on the middle of the shaft. Elevate the two end bearings and push down on the middle bearing. The weak side should be facing down. Try twising (turning) theshaft to confirm. Mark the strong side with a marking pen and test it a few times. You may also find some "secondary" spots on the shaft. This where the feel part comes into play.