1 - Know the other options
Get a sense of the pipeline. If this is the only job coming in the door this year, it's this, or find a new job. If this is one of 20 jobs, 19 of which are more interesting to you than this, it's a vastly different story.
Also - know the duration and the options for switching a consultant midstream. If you take the not-great gig, and a better-for-you gig comes in, can you switch?
Similarly - know your relative ranking compared to others in your team. If you are the guy with the least experience in project management, and this is a dry spell for project management, you may not have many options.
2 - Know the tradeoff from your boss' perspective and be willing to adapt.
Know both how frequent project management comes in, and it's billable advantage/disadvantage with technical work. If you are asking that you get work that is less profitable for the company, then are you prepared to take a pay cut?
What I've seen is that it's hard to substitute project management for technical work if technical work is what's called for, so be aware of the business case involved in pushing for the one kind of work.
3 - Assuming the odds are in your favor...
Once you know that project management is an advantage for the company as well as your personal interest, have a talk with your manager about how this job is not inline with your career goals. Unless you are willing to look for a new job, don't deliver the ultimatum "I simply will not do this job"... voice it more as a question and concern - "this job is a poor match for my career goals of project management, are there other options? What is the option to get experience later in my actual interest if I am a team player now?" Your boss won't be able to guarantee a future opportunity, but he can give you a sense of the options.