Do high heels increase female attractiveness in men only through indirect means? It seems widely accepted that, overall, men tend to find women in high heels more attractive.  (There will, of course, be many exceptions to this rule.)


  "High heels may well be the most potent aphrodisiac ever concocted." -- Rossi 1981


However, the increase in attraction seems to be only indirectly ascribed with wearing high heels.  Typically this is described along the lines: high heels cause a change in the posture of the female, which the male finds (sexually) attractive.


  Question: How can we exclude the possibility that the high heels themselves are not the main cause of the increase in attractiveness?


That is, how can we exclude the possibility that men, overall, primarily just like the sight of women in high heels, for some reason or another?

My thoughts:


If the increase in attractiveness were primarily due to these indirect factors, then we should see a comparable increase in attractiveness e.g. if a woman were merely to stand on a slope.  (Although, this would not account for the addition factors, such as gait, and the sound made when walking in high heels.)
There are things that women do, such as fingernail painting, which increases attractiveness, but (arguably) not sexual attractiveness.  It seems plausible that the "femininity" associated with wearing high heels (as with fingernail painting) could be a large factor in the increase in attractiveness.


References
Rossi WA. (1981) High heels: the agony and the extasy. Journal of the American Podiatry Association 71(12), 698-699.
It is probably quite simple to test whether high heels themselves are the main cause of the increase in attractiveness, or rather the changes to posture imposed by them - just let participants rate the attractiveness of women who do not wear high-heels, but, for instance, hold them in their hand. 

Alternatively, you could expose one half of your participants to high heels and the other half not. Afterwards let them rate pictures of women and compare the mean ratings of the groups. 

In principle, you could a multitude of experiments with women and high heels - as long as the women do not wear the high heels, you can exclude that the effect on posture explains your results. 

An alternative approach, suggested by Artem Kaznatcheev in the comments, would be to compare the attractiveness ratings on women with and without high heels while their feet are not visible (e.g., covered or removed from the picture). Finding the same rating difference like observed with visible feet would suggest an effect of posture caused by high heels, rather than high heels themselves. (Actually you would need at least an two-by-two design ([high-heel vs. no-high-heel] x [feet-visble vs. feet-invisble]) to draw this conclusion.)