Cam cream has an oil base to it, which means you need one of three things to remove it.
1) soap - it breaks down the oils in the same way washing up liquid does your fried breakfast pan.
2) other oil-based products, (as they dissolve into eachother) such as vaseline or moisturiser. Or WD40, although long term application may lead to health problems in later life.
3) Some alcohols will dissolve in fats such as cam cream making it easier to wipe off, but not all so you may have to experiment with babywipe brand to find one that suits.
In short, the science backs up the experience already stated here, and recommends giving it a good wipe with something creamy/fatty/alcoholic and then using soap to remove the remnants.
I found being strapped face up on the roof rack and being driven through the local car wash worked for me every time. For H&S purposes, the local Asda insisted that I wore a 'hard hat' peak to the rear, otherwise I risked invalidating their insurances.