First off, have you already seen Lime but don't want to incorporate that framework, since its entire purpose is to incorporate Tiled maps in Corona:
http://lime.outlawgametools.com/
In your searches of the Corona forums, did you find these threads?
http://developer.anscamobile.com/forum/2011/01/29/object-culling-render-process-when-not-content-area
http://developer.anscamobile.com/forum/2011/02/03/screen-culling
http://developer.anscamobile.com/forum/2011/03/24/tilemap-using-spritesheet-very-slow-device-any-help
A while ago someone had asked about developing efficient tile map performance/culling and I provided an example of one simple approach using quadrants to organize the tiles for efficiency. Then p120ph37 showed up with an even more efficient technique that changes the frame of the sprite objects without actually showing/hiding sprites.
What a coinciendence: just yesterday I saw this preview of the improved tiling performance in Corona's latest build.
http://www.youtube.com/watch?v=nzdjNDcn2gE