I would play a card game in this situation. Write your linking words on cards and go around the class holding them fanned out and face down. The student starts with a simple expression (to avoid shyness / confusion, you can make a separate set of initial phrase cards) and when they are done speaking it, they draw a random link card; they must make up the last part of the sentence on the fly, with feedback from the teacher.
You could start with just a few link words in your hand to choose from, and gradually expand the set as they become comfortable using them.
hope that helps.