Basically you need someone to drive your vehicle to the takeout and drop it off. Here's an example: Say a friend and I want to float from the Dam to Happy Hollow. If they are bringing a boat, we would leave my car at Happy Hollow and I would ride with them up to the dam. There we would put the boat in the water and park the truck. When we finish our float down the river, one person would take the car up to the dam and exchange it for the truck. Then we take out the boat, go get my car, and we're done.
There are people in the area that will run shuttles and they will usually charge $15 dollars or more depending on which float you are doing.
I'm sure some others might be able to provide details on who to call for shuttles.