A friend of mine started writing his predictions and putting them in sealed, dated envelopes. He said the 3rd time he pulled one out Carnac[1] style, management actually started listening to him. Nobody really got "I predicted this 18 months ago" but the theatrics apparently drove the point home.

1: https://en.wikipedia.org/wiki/Carnac_the_Magnificent

A dirty trick, but an effective one. May the fleas of a thousand camels infest you, and may your arms be to short too scratch.