Eric Cressey wrote up a nice article (with nice videos, as usual) about deadlifting when you can't pull from the floor.
How to Deadlift When You Can't Pull From the Floor
Another way I do this is to teach kettlebell sumo-style deadlifts from the top. I have the client lower the weight until just at the point when the back would round, and then come back up. This allows the weight to help pull them down towards good form, and allows them to get a training effect even before they have the mobility to get to a weight on the floor.
One other good thing about KB deadlifts from the top is that you can use light weights to see where there form breaks down without needing the mobility to get down to the floor first. You simply let them lower until they can't do it with good form, and then address the issues that you see stopping them.
Done correctly, the KB deadlift from the top will also mimic the form of a KB swing and of a snatch, jump, or hang clean - weight goes down, hips go back, knees unlock but don't start the motion, and weight is on the heels. Then you drive back to the top with your hips and lock out to a standing posture. This makes those lifts accessible to the trainee because you're teaching them the basic form right from the start.