No, I don't think there is.
But, leave it to the guys in the Penis Enlargment Think Tank to come up with one.
That they haven't shows 1) that most people want big penises and 2) most guys don't have them (yet).
If anyone was having a problem with the size of their penis, that they suppose it is too big, just like it being too small, it's usually more a pyschological issue than a physical one. A real support group - not necesarily most of this forum- and counseling can really break down barriers and help people with these issues point themsevles in the direction of the kind of life they would like to be living.
Additionally, if you find yourself a little bit too big for the one you love, there is an old maxim, namely "Lubricate & inebriate"
Now, while I am not advocating alchohol use, and certainly not its abuse, methods to calm both parters can do a lot toward making sexual contact more enjoyable for both. Olive oil, and a little wine have been staples of the Italian diet for centuries, and perhaps for more reasons than one. A couple having this sort of problem might also try valerian root, melatonin, or passion flower (not an aphrodisiac), catnip, camomile or mint tea.
Simply dimming the lights can make your big penis less intimidating and awkward to a small women, I can say from experience. For most of them, unlike many of us, sex "feels better than it looks". Maximize ways both of you can enjoy your penis and eachother, without it being a hurdle to overcome.
And remeber, the more natural and less chemical laden the lubrication is, the more pleasurable and less irritating it is to both partners. Always use one that is compatible with the safer sex method you are using.
As far as actually making your penis smaller, this is not something you want to do. Injury, tobacco, alchohol, high cholesterol, high blood pressure, high triglicerides, high blood sugar, sleep deprivation and depression among other things cause a sliding scale from a slightly less hard (and therefore smaller) erections to impotence. Don't let it get to this point.
If you wanted to make your penis slightly smaller than usual, I do have one recomendation. Take a cold bath. This doesn't just cause the "shrinkage" George Costanza made famous. It actually draws the blood to your body's core for a time, and away from your extremeties - fingers, toes, and penis. Your erection you will notice will not be quiet as big, just as it will be just a little bigger coming out of a hot bath.