Women can do it because they can attach erotic desire to personality traits. Men? Ha!
That's why most of us live within the narrow confines of our sexual bandwidth. The point was poignantly made by one gay guy who wrote to me:
"Guys nearly always want someone with their own body type, and I'll never have it. I'm a beanpole by nature: thousands of hours of weight training haven't turned me into a hunk, just made me less skinny. No reputable doctor will prescribe anabolic steroids to me, and I don't want to risk doing illicit steroids. Given the Gay Rules of Attraction, I know my chance of getting a studly boyfriend is slight-to-vanishing."
Can he change the body type he's attracted to? He tried going out with average-built guys and his libido took off like steel safe off a cliff. He even tried therapy. No go.
And no wonder. Going to therapy to change the kind of person you're attracted to is like going to therapy to change the kind of gender you're attracted to: The only positive change will be the therapist's income.
The sad truth is that most gay guys like their own body types (just like most guys like dating guys their own age, race and class). Still, the last time I looked up "most" in the dictionary it didn't say "All."
Physically opposite couples may be a minority but you do see them: Young with older, black with white, tall with short, bitter with stupid.
While you can't change your desire you can change your strategies. Many "body-reversed" couples aren't necessarily attracted to their physical opposites; they're attracted to certain emotional qualities that just so happen to be packaged in body types they're not particularly keen on. In other words, try being the kind of person anybody, your type or not, would want to be with: Enthusiastic, funny, confident, interesting.
HOWEVER.
Facts are facts. Gay men are not straight women. We can't (most of us anyways) reshape our desire to fit the contours of a personality trait. If we could, the porn industry would drop to its knees.