How to Prevent Lowpass/Highpass From Effecting Audio?

[Perfect Human Interface]

Okay, maybe a silly question (and a bad thread title), but say you want to put a lowpass/highpass function on your plugin, but you don't want it to effect the incoming audio at all unless the filter is turned down/up respectively (make sense?). Now, I can imagine a simple way of doing this by switching the audio signal path off from the filter when the knob is set to the min or max value, but I'm wondering if there's a better/cleaner way of doing this. It would be nice to have it completely seamless I guess. Has anyone done something like this? How did you go about it?

By the way, I'm handing out IOU's to everyone that's been helping me out. You guys are great.

[KG_is_back]

There is usually so little content below the minimal cutoff (15hz maybe) of LPF that even on sudden bypass the click will not be noticeable. If you want to be perfectly sure you can add a crossfade. This little thing should create seamless crossfade between two signals.
However if you hear a click between minimal cutoff and off-state, that means you have some stuff below the cutoff (usually DC) that you probably wanna get rid off. the same applies to LPF too.