We perform a tomographic cross-correlation analysis of archival FIRAS data and the BOSS galaxy redshift survey to constrain the amplitude of [CII] $^2P_{3/2}\rightarrow$ $^2P_{1/2}$ fine structure emission. Our analysis employs spherical harmonic tomography (SHT), which is based on the angular cross-power spectrum between FIRAS maps and BOSS galaxy over-densities at each pair of redshift bins, over a redshift range of $0.24Comment: 20 pages, 14 figures, accepted by MNRAS