While in McKinney, we also dug up Jan's old paper hearts to make a banner for her kitchen window. Again, we just used some hot glue to adhere them to a length of jute. We added a few single thickness paper hearts, in a smaller size, to balance it out.
Look for great pages from old children's books and the heart is already decorated for you.
A burlap heart wearing a tutu with buttons, like this one from "My Favorite Room", would look good on a banner too.
Or print and cut out some Valentine postcards from the Graphics Fairy. These are just a few of the many Valentine graphics you can find there. Wouldn't these look great on a banner, interspersed with some paper hearts?
I'd love to see what you come up with!