At the first round I judged this year I was given about 2 of the plastic corks meaning the expectation was that the bottle sit (with the original cap back on it as well as it will go) until I am sure it is a mini-bos beer. But how do you know which two (or three) are mini-bos beers until you are done with all of them?
Here's what I do:
1. Open bottle (me, not the steward).
2. Pour n beers. Maybe two fingers tall.
3. Immediately recap.
4. Judge beer.
5a. If beer scores in top 3, put the bottle away (cold).
5b. If the beer isn't in the top 3, pull and reuse the cap.
5c. If the beer bumps something else out of the top 3, pull that cap and toss the beer.
6. At the end of the flight, take your top 3 out of storage and see if you want them.
If you wait until after you judge the beer to decide if you want to recap, then you've blown it. A second bottle is better, but this is how to make the best of it with one bottle.