So let's say my sprite sheet has 3 sprites in one row. One sprite is 64 pixels wide and high. When that is combined my sheet would be 192 pixels wide and 64 high. So from that, how am I supposed to make it's dimensions POT without stretching sprites inside?
Just add extra, blank space.
A 256x64 texture is a "power of two" texture and can fit your three sprites packed into the left (or right, if you really prefer) side of the image. You'll have an extra 64x64 block of empty space in the texture you can fill with additional data as you need to. Or just leave blank.