I did this last year, GVA-IAD-ROA. I informed the agent in GVA at check in that I wanted my bags checked ONLY to Dulles (since there were liquids I was bringing for a friend back home, who planned to meet me at IAD before my connection). Worked perfectly- I went through the IAB just as if I had no connection, met my friend, and checked my bags for the domestic flight just like normal. Of course, if you're subject to bag fees this may not be the best course of action, but staying at midfield will require you to go through security again.