tk2d isn't built for this, it will successfully import the image as a tilemap and optimise the tiles, removing duplicate tiles in the atlas, and it'll be useful in that regard. Eg. your atlas will fit in a 256x512 image no bother, but internally it still treats these as unique tiles, i.e. collision will have to be set up on individiual tiles in the sprite collection editor.
Unfortunately this is a fringe use case, most people don't want to reuse existing maps, and we dont have any plans to support that.