After some instruction and practice with circumlocution techniques, I have found that students find it much easier to communicate complex ideas with their limited L2 vocabularies. I have also found that I get a lot less of that "How do you say _____ in Spanish?" question and feel much less like a human dictionary.
So, here is what I have found to be the perfect way to teach this concept. Find a copy of the English board game "Taboo". It probably available at a local store or on Amazon. The game contains cards with a word featured on the top that one person must get another person to say. The catch? There are also 5 or 6 of the most common words associated with that word listed on the card and none of those are allowed to be used to help the other person guess. For example, if someone is trying to get their partner to guess the word "bride", the card may list groom, wedding, marry, and white as words that can not be used. This forces the person to use circumlocution by talking around those 4 words. The person might have to say "she walks down the aisle and says I do" to get them to guess the word "bride".
Once the students have played a few rounds we talk about what strategies they used to get their partner to guess the words. I usually speak to the pairs that won first as they may have more insight. After we have discussed some strategies, I show the students some words in English that I know they do not know how to say in Spanish. I ask them to share ideas as to how else they could describe the item so that someone could guess what they were talking about. For example, if I show them the word "high heel" they might suggest that they could describe it as a "zapato alto". If I show them a skunk, they might offer "un animal blanco, negro, y aspestoso".
As we continue to speak throughout our classes, I remind them to use circumlocution when they want to say something that they don't have the words for. As time goes on and their vocabulary grows, their need for circumlocution will be less and less. Until then, I feel that knowing some techniques and strategies will encourage students to practice speaking and play with the language. See what works to communicate your idea and what doesn't. After all, if they're stuck in a public restroom in Mexico and there's no toilet paper, they're going to need to figure out SOMETHING!
Here is a link to an online version of the game so that you can get some ideas of what the cards are like:
Taboo Game Online