Yes, you will have to mash flaked rye. But honestly, if you are only going to add 8 oz, I bet the flavour of it won't even be detectable in your beer. There are LOTS of threads and recipes here on using rye in various types of brews. While there is a lot of personal preference out there, a number of people advocate using both flaked and malted rye (often at around 30% of the grainbill) in their recipes. If you are brewing a roggenbier to the BJCP guidelines, then you need at least 50% rye as your base.
Anyways, you might try getting a pound or two of malted rye and do a mini mash with it. It has enough DP to convert itself plus, so you could easily add some flaked rye, as well, to intensify the rye flavour.
Here is a good thread on the difference between flaked and malted rye:
http://www.homebrewtalk.com/f12/rye-flaked-vs-malted-21823/
P.S. My next brew is going to be a rye beer, too!
