You can simulate bigger maps by shrinking all of your units, doodads, and destructibles. For example, make everything half size and your 480 x 480 map effectively becomes 960 x 960. However, creating such a ridiculously big map has some drawbacks:
(a) It involves a Herculanean effort;
(b) You will probably end up zooming the in-game camera to counter all of the object shrinkage, but that can make the tileset textures look pretty bad (although you can get around this by using custom tilesets); and
(c) Your final product will probably suffer from serious performance issues to the point of being unplayable (although there are ways of getting around some of these).