How can I hang a plant below an eave with vinyl perforated soffit panels?

Hi! I have a deck on the back of my house and there is a perfect corner where the house meets the deck and a hanging plant would look great. However, the eave (or soffit) has these vinyl perforated panels and I don’t know what is inside them (besides the roof, of course). Here is an image:

http://www.biytoday.com/Soffit2.jpg

I don’t want to damage anything, and I don’t want to just randomly jab a threaded hook up there hoping to hit a beam. Any idea how I could make this happen? Thanks!