  We have implemented a novel method to create simulated [CII] emission line
intensity mapping (LIM) data cubes using COSMOS 2020 galaxy catalogue data. It
allows us to provide solid lower limits for previous simulation-based model
predictions and the expected signal strength of upcoming surveys. We applied
[CII]158$\mu$m luminosity models to COSMOS 2020 to create LIM cubes covering a
1.2$\times$1.2 deg$^2$ sky area. These models were derived using galaxy bulk
property data from the ALPINE-ALMA survey over the redshift range $4.4<z<5.9$,
while additional models were taken from the literature. The cubes cover
$3.42<z<3.87$, $4.14<z<4.76$, $5.34<z<6.31$, and $6.75<z<8.27$, matched to
planned observations from the EoR-Spec module of the Prime-Cam instrument in
the Fred Young Submillimeter Telescope (FYST). We also created predictions
including additional galaxies below current detection limits by `extrapolating'
from the faint end of the COSMOS 2020 luminosity function, comparing these to
predictions from the literature. In addition, we computed signal-to-noise (S/N)
ratios for the power spectra, using parameters from the planned FYST survey
with predicted instrumental noise levels. We find lower limits for the expected
power spectrum using the likely incomplete empirical data: when normalised by
$2\pi^2$, the amplitudes at $k$ = 1 Mpc$^{-1}$ are 3.06$\times$10$^7$,
1.43$\times$10$^7$, 9.80$\times$10$^5$, 2.77$\times$10$^5$ (Jy sr$^{-1}$)$^2$
for the aforementioned redshift ranges. For the extrapolated sample, the power
spectra are consistent with prior predictions, indicating that extrapolation is
a viable method for creating mock LIM cubes. In this case, we expect a result
of S/N>1 when using FYST parameters. However, our high-redshift results remain
inconclusive because of the poor completeness of COSMOS 2020 at $z$>6.3. These
predictions will be improved on the basis of future JWST data.
