I've never needed to do this, but if I did, there's a few different ways to go about it.

It would depend a lot on how wet the clothing needed to be, and what type of clothing it is. A heavy coat is going to look and behave completely different when wet than a t-shirt or a pair of jeans would. The coat would keep most of its shape due to all the padding inside, but a shirt or pants would be practically skin tight. 

Again, would depend on a lot of factors, so you should be a bit more specific on the look you're trying to acheive. 

A soaked shirt could be done as a texture over the figure's skin texture with proper displacement maps for wrinkles.

Or you could take the shirt model into the cloth room and shrink-wrap it to the figure, then model in the wrinkles with the morph brush or in a modeling app. 

Dynamic clothing would likely be easier to work with for acheiving the right look than conforming clothing would, but either way you're probably going to have to create a lot of custom morphs to make it look believable.

 

~Shane