First I popped to Argos and bought their shoe holder, it's the cheap 6.99 one which is made out of fabric; this is the best kind as it allows drainage. Along with that I bought 30litres of basket compost, this has moisture retaining crystals in it which is ideal for these small exposed pockets as they could dry out quickly. Finally I popped to my local Sainsbury's and picked up two packs of their living salad, basically lettuce already growing in plugs and it only cost a pound! All in all this project cost me less than 15.00 to set up.
Hang up the shoe holder using the metal hooks provided, you will need to adjust them so they don't stretch out and let the shoe rack slip. The weight of the compost, water and growing plant could cause that to happen. If you have the ability to, screw it in to the door for even more sturdiness.
Fill up the pockets with the compost.
Water them, ready for planting and then put in the plugs of lettuce.
They will need regular watering, as you would a hanging basket. I'm also not sure on how the slugs will treat them, hopefully they will ignore them. I've just remembered that I left the other pack of lettuce on the floor so they may have eaten that as a sacrificial feast.
If you have a go at this, I'd love to hear from you.