What’s the best way to tactfully handle situations where a Servicemember brings an inappropriately dressed guest to a formal military ball?

I always briefed my soldiers and had all the NCOs inspected and inspecting their soldiers to make sure we were up to snuff.
I also made sure the wifes club had a little tête-à-tête's with the dates of the soldiers where they gave them advice, loaned them appropriate attire, took them shopping and showed them how-to use their spoons, prepared their hair etc, etc.
We also helped them after arrival to ensure they and their dates were able to meet with everyone.
Getting together and passing along traditions is what it's all about. Making it a feared event isn't.

I want to see the picture :)

I can tell you how it is handled after the fact.
https://d26horl2n8pviu.cloudfront.net/pictures/images/000/004/050/large_v3/elegance-formal-class-military-demotivational-poster [login to see] .jpg? [login to see]
These pictures are from the '98 or '99 USASOC Christmas ball.
The guy with the high and tight was one of our BN Staff officers.
His wife chose poorly with the dress, and while on the dance floor, removed all doubt as to whether she was going commando.
The officer was permanently banned from all USASFC and USASOC functions, and was transferred out of the unit ahead of schedule.
I didn't attend that event, I saw the pictures in a forwarded email that most of Campbell and the Army saw by mid-January.