When you get to the Groundbreaker you will get the holographic disguise as part of the story in the captains quarters.
With this you can enter restricted areas disguised. As you move the disguise starts to fail and if seen will have to do a speech skill check to remain undetected. You can do 3 of these before your cover is blown.
Go to the medical bay (on the left in the promenade) pick up the ID from the table in back and go into the restricted area, there is a guard here so run around until the meter expires and you get skill checked. You will need to have lie, intimidate or persuade at 15 to pass it, subsequent checks need higher level skill so simply exit and repeat. Having Ellie with you will give you +9 in lie, and various armor and helmets can give you +5 . You can of course make a save to reload later and respec to get the points too.
You can do this naturally of the course of the game but this is a way to get it out of the way easily.
NOTE: This has to be done in one save, reloading after say doing 10 will reset the count to what ever it was before saving.
EDIT: Caution if doing this on supernova, your stats will drop as you get tired, thirsty and hungry and could result in you not being able to pass a check so make sure you save before doing this.