Indeed, in chapter 6 ("Human Pain") of The Problem of Pain, Lewis explicitly connects the idea to Aristotle:
Kant thought that no action had moral value unless it were done out of pure reverence for the moral law, that is, without inclination, and he has been accused of a 'morbid frame of mind' which measures the value of an act by its unpleasantness. All popular opinion is, indeed, on Kant's side. The people never admire a man for doing something he likes: the very words 'But he likes it' imply the corollary 'And therefore it has no merit'. Yet against Kant stands the obvious truth, noted by Aristotle, that the more virtuous a man becomes the more he enjoys virtuous actions.
But probably his most extensive treatment of the idea comes in chapter 9 ("Charity") of book III ("Christian Behaviour") of Mere Christianity, in which he writes:
It would be quite wrong to think that the way to become charitable is to sit trying to manufacture affectionate feelings. Some people are "cold" by temperament; that may be a misfortune for them, but it is no more a sin than having a bad digestion is a sin; and it does not cut them out from the chance, or excuse them from the duty, of learning charity. The rule for all of us is perfectly simple. Do not waste time bothering whether you "love" your neighbour; act as if you did. As soon as we do this we find one of the great secrets. When you are behaving as if you loved someone, you will presently come to love him. If you injure someone you dislike, you will find yourself disliking him more. If you do him a good turn, you will find yourself disliking him less. ...
The Germans, perhaps, at first ill-treated the Jews because they hated them: afterwards they hated them much more because they had ill-treated them. The more cruel you are, the more you will hate; and the more you hate, the more cruel you will become—and so on in a vicious circle for ever.
Good and evil both increase at compound interest. That is why the little decisions you and I make every day are of such infinite importance. The smallest good act today is the capture of a strategic point from which, a few months later, you may be able to go on to victories you never dreamed of. An apparently trivial indulgence in lust or anger today is the loss of a ridge or railway line or bridgehead from which the enemy may launch an attack otherwise impossible.
Some writers use the word charity to describe not only Christian love between human beings, but also God's love for man and man's love for God. About the second of these two, people are often worried. They are told they ought to love God. They cannot find any such feeling in themselves. What are they to do? The answer is the same as before. Act as if you did. Do not sit trying to manufacture feelings. Ask yourself, "If I were sure that I loved God, what would I do?" When you have found the answer, go and do it.