This is the process, with pictures, of how the LEDs were put onto the back board.
Firstly I measured out the holes. There will be one LED every 2cm, and there are two lines of 60 LEDs.
I then carefully drill holes in the back (through the display board) using a 6.5mm drill bit, being careful not to catch the fabric on the other side, as this would crease the fabric, and sacrifice aesthetics.
I then used a craft knife and a pair of scissors on the other side of the board to carefully cut holes in the fabric for the LEDs to fit through.
The LEDs themselves are firstly put into little holders, so they look better. These are 8mm wide at their widest point, but require a 6.5-7mm drill hole, and hold a 5mm LED.
I then put the LEDs into the holes, with the positive and negative ends all matching up at the back. This will help when it comes to soldering.
And here is a picture of the front when all the LEDs are in place: