you would have to group the bitmaps into one imagefile before compiling it to a bitmap.
each image would be next to (or above\below) another image within one image plate, and each image within that would need a blue border at least one pixel wide (at pure blue, 0, 0, 255)
or here is an example image:

Each image is still 128 x 128 pixels wide, as the blue borders don't count against the power of two limit. you can add as many images as you want, but you begin to have issues above 20 or so (sequence indexes aren't read properly)
Edited by Jesse on Jul 27, 2014 at 08:13 AM