Ideas of how to make a fake heart shaped topiary?

My fiance and I are getting married in October and we're doing kind of a Tim Burton theme. We've been looking for a heart shaped topiary, we want a rather large one.

We were thinking about buying styrofoam blocks. I've seen them at stores. They're maybe 2 feet long and about 3 inch wide. We were going to cut and glue them together to form the heart in the size we want. then glue artificial ivy of some sort all over it. Not sure how well it will work, we're going to try it.