+1 for the Quartet Harness, the only problem is that if you don't already have it, you need to remove the left fairing to install it.
Otherwise, you could tap into the running light (I wouldn't touch the brake light for this) and install a relay so that the relay gets 'turned on' with the key, yet pulls it's juice from the battery. Then put in a fuse box from the relay and add all the farkles you want. As for me, I still put in the quartet harness.