Ah, yes! I've acquired the liking to smearing vaseline on things too! Well, my camera officially smells like Vick's. I've been experimenting ideas to mess with my lens on my Polaroid. My crappy digital camera too! Very good work my friend.
yeah, I've been rather interested in manipulating things directly through the lens too I keep looking for old bits of plastic that I can melt and tape to the lens. There are a few sites online that show you how to make a homemade lensbaby too so I'm gathering supplies left and right.
I put it on right before I take a photo, because if you leave it in a bag or carry it around too long dust and all kinds of gross dirt gets stuck to it (though that in itself could make some interesting patterns around the edge!) ..I just dip my pinky finger into the jar of it and rub it around the edges probably about a 1/3 of the way in.
you can also do chapstick. I took a few photos with pink chapstick around the edge and it sort of tinted the color, pretty neat