I'm not sure if it is actually his silhouette (though it looks pretty close), but I always connected that line to Hammer Groupie #3, who sings the next line in the song, and is quite obviously in love with Captain Hammer.

It almost looks like a standard head-shot pose.

Doubtful it's Mr. Harris. Needs a longer neck and a more pronounced jaw.

I'm going to rule out Mr. Whedon (the Joss one). The cheeks need to be chubbier and the hair always goes down to the ears on that guy (unless they cropped it like that on purpose).

Groupie #3 is plausible, but the posted headshot of Steve Berg doesn't match. I can't completely rule out CH except for the same hair issue as the previous.

Pink Pummeler's ears stick out too far.

Adam Baldwin is also plausible, but his ears kinda point out at the top.

Tahmoh Pinikett (the guy with the bromance from Mr. Whedon) is plausible.

I'm going to have to say Groupie #3 as Jazzy stated unless I spot a specific picture that could have been used.

Wouldn't it be ironic if it was David Fury? (Face doesn't look long enough to me.)

I'd like to throw Doug Petrie, one of the other Mr. Whedons (the Zack one), Rob Reinis and Lance Lanfear into the hat (and the possibility of a photo from a younger Mr. Whedon).