Maybe some kind of plants?
In the summer, you might be able to grow vines (peas, beans, cucumbers, squash, etc.)
Given the time of year, maybe some imitation vines? Holly would look nice and Christmas-y.
Cornstalks or stacks of hay bales for Thanksgiving?
A row of Christmas trees? (Artificial or real, depending on what's available and how long you need it to last.)
Big inflatable holiday decorations? Sheets of white fluffy fabric to be fake "snow"?
One of those lit-up nets that people put over bushes? That might not be opaque enough, but lit-up things sometimes play funny tricks on the eyes, so it might have a chance of working.
A big flag? Or several flags?
Obviously, I'm thinking of things that could pretend to be there for another purpose: gardening, landscaping, decoration, etc. Maybe look around the area at what other people have, and consider if any of them would work for you.