A technique for counteracting lustful (or greedy) feelings that has worked well for me is to look more closely at the features/qualities of whoever (or whatever) I find myself attracted to. I find that lustful thoughts are often as much, or more, about craving for a perception (saññā) or mental formation (saṅkhāra) of beauty that my mind is fabricating as for the actual sense object. When I just quickly see an attractive person, it's like my mind fills in the details with what it wants to see, and it's easy to feel lust. However, the closer I look, the more obvious that person's realities become (e.g., unequal proportions, rolls of fat, wrinkled skin, a few grey hairs, worn clothes, smudged make-up, etc.), and the harder it is to feel lust. Don't stare impolitely, of course, but look past the make-up, hair styles, shapes of clothing, etc.
Anyone's body can be reduced to neither-attractive-nor-unattractive components (skin, hair, muscle, fat, bone, glands, organs, etc.). Reading about the science of anatomy is also a good way to learn how to mentally reduce bodies to components. For example, eye color is just melanin + light refraction; breasts are glandular, fat, and connective tissues, and both/all sexes have the same tissues to some degree; sex organs diverge in the womb from a common template; etc. I once wrote a more detailed blog post about this, here: http://mindstring.net/2014/03/30/reflections-on-repulsiveness/
. Bodies are just biological hardware (rupa) -- a substrate for the arising of sensations, perceptions, mental formations, and consciousness (i.e., the five khandhas).
I find that a good way to see differences between internal and external things is to compare how people or things look in dreams vs. how they look when awake. I've seen/fabricated images of people in dreams that are much more beautiful than any person I've ever seen when awake. Practicing lucid dreaming (e.g., trying to stop and examine things in dreams, to control what happens in dreams, or to create and destroy inanimate objects in dreams), keeping a dream journal, attaching labels to dreams for easier remembering, etc. can help one see dreams more clearly.
I agree that reflecting too much on repulsiveness can take one down a dark mental path. Focusing on tiny details can lead to insights, but can also be overwhelming and exhausting. These things are all just mental techniques, treatments, or medicines. Like any medicine, one should take only enough to get well, and taking too much can be harmful.
Hope this helps