Fall asleep while on it's back being rubbed is a good sign

It is also possible (and I think preferable) to train animals without food as a treat. I have trained lots of types of animals to to all sorts of stuff, including rats, without treats. If you use "clicker" training, I have been told to use those baby food lids instead of the clickers made for dogs because the dog clickers are too loud for rats (those are what I use but because they are free). I do lots of my training without the clicker though.

To start, I get the animal very used to me holding the animal in all sorts of positions (while petting the animal and rubbing in small circles) If you can get the critter to fall asleep while on it's back being rubbed, your on the right track. With the animal completely trusting you, you can show it exactly what you want it to do (I use a pencil sized foam or rubber stick - like those "mechanical erasor" inserts - with rodents to move paws). While you are showing the movement, say the name of that action and also have a hand signal for that movement that you are also doing. Then with a clicker make the click. When the animal does that action again, click and say the action's name and do the hand signal. Consistancy is very important. To clicker train rodents with treats, I attach a spoon to the clicker and put the treat on the spoon. Start simple actions for each command and then make those actions a little more complex. Remember a rat will likely only remember a couple dozen commands so decide before hand what commands you are going to use and write them down so you can be consistant. The key as far as I can tell, is to really love the animal first and the tricks are just a little game you add to thier petting time.