Double-blind review: submit a follow-up paper in a very short time
I've been in a similar situation before. After consulting with the conference chair, we decided to place an anonymized version of the accepted paper in a dropbox folder and cite it anonymously as our own with a link to that dropbox file in the reference. I also added a footnote in the paper to explain that this previous work is accepted but not yet published, and how this previous work contributed something totally different from the work presented in the paper.