Right now, Lightroom isn't the program for special effects. I've little doubt such things will come in due course, but right now there are a number of things that you can do - with a little bit of wine-crazed ingenuity.

This image was output directly from Lightroom using the same original as this but was produced by applying a preset that modified the Tone Curve.

But the curve's shape is not one you can do within Lightroom - it was created in ACR4 using its Point Curve and applied to a DNG file. This was imported into Lightroom, which read the curve, and I then saved a Develop preset with the effect. To my eyes it's some distance from the ideal solarization, but interesting nonetheless.

Here's John's solarization preset.