They did consider various options, but nothing met the requirements.
"In short, there were possible methods, but nothing simple and light and certain. And the rover developers didn't have the time, the mass, or the leeway to experiment. Attractive though the idea was, this mission couldn't afford to try it."
http://www.newscientist.com/blogs/shortsharpscience/2008/11/...
They did consider various options, but nothing met the requirements.
"In short, there were possible methods, but nothing simple and light and certain. And the rover developers didn't have the time, the mass, or the leeway to experiment. Attractive though the idea was, this mission couldn't afford to try it."