Have you tried setting a background image on the input element? Your background image could be the line.
i.e.
input {
background: url(path/to/image.png) repeat-x;
}
EDIT:
I've had a quick play with this and have got something up and running here: http://jsfiddle.net/qUc9Y/
I've wrapped the input in another element (fieldset.input-wrapper) and moved your CSS transitions to this new element. I've pushed the input down relatively 10px so it overhangs the shadow created by the container. I've set the background of the input to transparent so the box shadows on the .input-wrapper are visible through it.
Finally, I've added some quick jQuery so that when the input is hovered, the css transitions are applied to the new .input-wrapper container (i.e. the input's parent). You should be able to do the same for focus/blur.
I hope this helps.
EDIT 2:
The focus state should now work too, see http://jsfiddle.net/yZ3uw/14/ .