Putting a widget as overlay on header image

Is there an easy way of putting an image on top of (i.e. overlay) the header image. e.g. I’d like to put the search widget on the right hand bottom corner of the header image.

I am using Weaver theme, which allows adding all sorts of CSS code from the admin panel as well as a whole host of “sidebars”.

However, I suppose my question applies equally to any theme…including TwentyTen…