I want to be able to track the usage of each device connecting to our router so we can split up the ISP bill by usage. Can dd-wrt or tomato provide the stats I'd need to do this?

Update:
After a bit of googling I'm aware of a much better answer than the current one. However I suspect there's probably more answers out there for other firmwares so in the interests of getting a more diverse set of answers—­and, I'll admit, because I'm getting tired of reading through obtuse firmware documentation—I've put up a bounty.

If the only answer added is the one I've found I'll be happy to accept it for the bounty, otherwise I'll add it and accept it myself, but I'm hoping for an even better answer, or at least some options for other firmwares as from looking I've seen a few other people have asked for this and there doesn't appear to be a definitive answer, let's make this it!

Go lazywebs!

(Sorry. I've always wanted to say that.)