what do you want to grow ? Vegetables, annuals, perennials ? You can always select plants that are more tropical and typically dont grow in your area.

Consider different or unusual containers.

I'm just exploring different forums, so I know nothing about balcony gardening. But, are you allowed to construct extensions off of the bannister to allow vines to grow out from your balcony's limited space? I lived briefly in an apartment and hung a bird feeder that extended out a few feet. If you have a counter weight that is heavy enough, and support structure that is strong enough, you could expand the growing space considerably. I don't know if that would be unique, but it might expand your possibilities.

Maybe hang colored glass balls, or mosaic planters with mirrors to reflect sunlight and the colors of your plants. Planters made from Hypertufa or papercrete might reduce the weight of the planters to allow for more creative uses. Good luck.

Martha