Indeed! There's actually been a lengthy discussion of this subject on poopreport. There are mechanical devices that allow this, but if you want to do it the old-fashioned way, I found the following advice from a website that no longer exists(the link takes you to an archived version of said page):

Finger-assist method

1. Wash or wipe your hands clean with a moist towellette.

2. Adjust clothing. Pants should be pulled down in front a few inches. Skirts should be lifted. Underwear should be pulled down at the waistband or move the fabric at the crotch to one side.

3. Wipe your labia area clean.

4. Using either hand, make a 'V' with your first and second finger and spread the inside of your labia minora. (the INNER lips) Beginners may want to try using the fingers from both hands for better control.

5. Lift to the desired angle, then pee. (If you don't spread and lift, it could run down your leg.)

6. Wipe your labia if necessary.

7. Wash your hands and you're done!

I'm pretty sure a woman wrote this, since most of us guys would probably be like "labi-what?". I could see how such a skill could come in handy for just such a situation. Plus if you tried this in the guy's restroom I'm sure everyone would be so impressed we could more than forgive you for going in the wrong restroom! (Though we almost always forgive the ladies who "borrow" the guy's restroom anyways.) Long lines always seem to form at the ladies' restroom but almost never at the guys' (unless of course 20 of us from a weekend pee workshop are all going in there at once for the practice!) So I think most guys are understanding of the women who are desperate, especially the pretty ones!

I, Nate B. (a.k.a. Latus Rectum), on this 30th day of the month of May in the 2006th year of our Lord, do hereby declare myself to be a Shameless Shitter. I hold these truths to be self-evident, that all humans are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are:
- The right to enter a bathroom unashamedly and empty their colon, bladder, or stomach as they find it necessary without reservation - anytime, anywhere, whether by urinal or by stall (as appropriate to the bodily function), whether by standing, sitting, kneeling or squatting, regardless of how bad it may smell or how far the smell may drift.
- The right to be afforded privacy. If any person wishes to use this time for quiet introspection, no one shall disturb them.
- The right to be granted access to and use in any appropriate manner a bathroom wherever and whenever this becomes necessary.
- The right not to be subjected to any form of turd terrorism, nor any act that violates the sanctity of the bathroom, and neither to be judged for any appropriate use of the bathroom on their part. No one shall be held responsible nor condemened for any smell or sound which is produced as a result of a necessary bodily function!

I do solemly pledge to do everything in my power to uphold the Four Sacred Freedoms of Shameless Shitting, and do everything in my power to protect and prevent the persecution and oppression of any and all shitters by anyone who would attempt to deny them the Four Sacred Freedoms of Shameless Shitting. Lastly I pledge never to regard a natural bodily function performed appropriately in any bathroom, either of mine or someone else's, as shameful, indecent or wrong in any way, regardless of the nature of the bodily function or severity of the smell, be it diarrhea, vomiting, flatulence, or any other natural bodily function. The natural and unavoidable workings of a person's body shall not be regarded as a reflection upon their personality, hygiene, strength or character in any way whatsoever. I do hold this to be a fundamental and self-evident truth for all humanity.

-- Latus Rectum