I use Dimensions for something similar to what you are wanting to do. The key is when you set up the items in your system, you set the dimensions.
For example, I have an expense called tolls and I need to track how much each of my trucks has spent in tolls. So what I have done is created an item for tolls that is specific to each truck. Item code is TOA1234 and in the item screen you can assign that item to a specific dimension. It might be a pain later on when I start getting to 20 or even 50 trucks to have 50 different item numbers for each item I need to separate out, but by having a simple stream line way of creating the item codes anyone can figure out which time goes to who. I also have a corresponding account for each truck as well.
Now when I run a profit and loss report and select one of the dimensions, I am able to get a breakdown for that specific truck.
Now there might be a better way to use dimensions than how I use it now, but so far this was the best way I could come up with.