A regular practice is what helps you master the language, but from my experience sometimes there are occasions when you can't find time to really sit down and do a full lesson to gain extra 10 points. This can be also true if you ever faced lessons where your answers are not accepted for this or that reason and you have to learn it exactly the way Duo wants you to respond. Again this takes time... time...time and I can tell you how it feels to loose 30 and more day streak...
So what you can do is...quickly go to Vocabulary, pick a weak word and click
practice word. Most of the time it has two or three exercises (instead of 20 like in a lesson) that you have to do and plus the number of hearts are always more than enough so that way you should be pretty much able to gain 2 points in 2 minutes.
That means you doesn't really cheat the system as you did at least something for your language but the result will be that at the end you are happy for not loosing you streak, and more importantly the owl is happy because you practiced a little :)
P.S. This new streak freezers which I don't have yet could be be another solution to this...
Yes, they could help, but they are quite "expensive" as in lingot currency. So your way is not cheating in my opinion. I suggest you only use the streak freezes for when you are going somewhere and you are 100% sure you can't go on.
You can just click the "practise skill" button and do a couple of questions - this is what I do when I have absolutely no time to a lesson. It's still practice, so I don't see how it matters.