Tuxedos. To get them into the premiere wearing military uniforms with all the military there would've been suicide. But going as members of the German film industry, they wear tuxedos and fit in with everybody else.
18 seconds sound clip from the Inglourious Basterds movie soundboard.
You can hear this line at 01:39:23 in the Blu-ray version of the movie.
Quote context
[...]
- The Englishman gave himself away.
- I arranged for the tailor to fit three tuxedos tonight.
- How'd you intend to get them in that premiere?
- You still get us in that premiere?
[...]