There are several leave-in conditioners. Here are just some that come up on an Amazon search:
Amazon.com: dog conditioner leave in
I'm sure there are others, too.
With that said - I use the people kind (for now). I've read that you should always use a dog shampoo because of the ph balance or something but that conditioners are fine if they are the human kind. Anyone know if this is right or if I misread??