R: Gaps between specific bars in ggplot

I have this bar graph.

I generate the graph with this code:

# Speedup Graph
  p <- ggplot(speedup_df, aes(x= benchmark, y = speedup, fill = factor(technique))) +
    geom_bar(stat = "identity", position = "dodge", width = 0.7) +
    scale_fill_discrete(name="Technique", labels=c("No Compression", "Compression Perfect", "Compression BDI", "Precompression BDI Hash",
                                               "Precompression BDI Similarity", "Compression CPack", "Precompression CPack Hash",
                                               "Precompression CPack Similarity", "Compression FPCD", "Precompression FPCD Hash",
                                               "Precompression FPCD Similarity")) +
    labs(title = plot_name, y="Speedup", x="Benchmarks") +
    coord_cartesian(ylim=c(min(speedup_df$speedup), max(speedup_df$speedup))) +
    theme(axis.text.x = element_text(angle=45, size=10, hjust=1)) +
    geom_text(data=speedup_df, aes(label=sprintf("%0.4f", round(speedup, digits = 4)), fontface = "bold"), size = 5, position=position_dodge(width=0.7), 
                               hjust=0.5, vjust=-0.7)

I want to insert gaps between the bars at arbitrary points. For example I want to have a gap before and after all the "BDI" bars. I tried using breaks in scale_fill_discrete but I get the error that they need to be the same number as the labels.