From an article at EW – Dr Horrible: An oral history

Fillion That is my friend PJ Haarsma. I called him up and I said ”Can you make me a thing? That looks like a thing?” Twenty minutes later he says, ”Check out this website. You can call it up on your iPhone and you have a Dr. Horrible van remote.” At Comic-Con, I’m going to release the Website that has the Dr. Horrible van remote.

It’s a lovely article full of fun stuff from Joss, Felicia, Nathan, Neil, Jed and Maurissa, go read the lot.

ETA: Dr Horrible van remote site (linked by highandrandom on Whedonesque)