Reusing previous review for similar paper
Open your review with something along the lines of: 

I reviewed an earlier version of this work (entitled previous_title), which was submitted to conference_name. The authors have since added a substantial amount of new material and have taken into account some of my previous suggestions. However, many of the issues I previously raised have not been addressed. What follows repeats much of what appeared in my earlier review.

In addition (and if appropriate), you might like to add something along the following lines: If the authors address the issues that I have previously raised, then I'll consider the new material in more detail. As it stands, I consider the previously identified issues sufficient to recommend rejection.