Now, this isn't my idea, but I want to see if it's any good.
Basically, the idea is that one could potentially befuddle the Borg's adaptive shields by using that adaptability against them... somehow make them believe a different weapon on a different frequency is being fired at them. Thus, they adapt to a disruptor blast, but get hit by a phaser instead. The false readings would of course be totally randomized. Good idea? Bad idea? Just give up and try hitting them with a baseball bat instead?