You can make a half heart with your hand and have a photo of you two putting your hands together (not touching) to make a whole heart. Maybe use a stuffed heart and hold it together (cliche but it might look cute). If both of you have a common hobby or favorite character or tv show you can use a plushy or themed items. Maybe use a small tree and have one of you on each side, and hands on the center of the trunk at face level (so you get faces and the ring in the photo). If your shadows are allowed to touch I think you could create some interesting photos.