  Observations the Sun's photospheric magnetic field are often confined to the
Sun-Earth line. Surface flux transport (SFT) models, such as the Advective Flux
Transport (AFT) model, simulate the evolution of the photospheric magnetic
field to produce magnetic maps over the entire surface of the Sun. While these
models are able to evolve active regions that transit the near-side of the Sun,
new far-side side flux emergence is typically neglected. We demonstrate a new
method for creating improved maps of magnetic field over the Sun's entire
photosphere using data obtained by the STEREO mission. The STEREO He II 304 \AA
intensity images are used to infer the time, location, and total unsigned
magnetic flux of far-side active regions. We have developed and automatic
detection algorithm for finding and ingesting new far-side active region
emergence into the AFT model. We conduct a series of simulations to investigate
the impact of including active region emergence in AFT, both with and without
data assimilation of magnetograms. We find that while the He II 304 \AA can be
used to improve surface flux models, but care must taken to mitigate intensity
surges from flaring events. We estimate that during Solar Cycle 24 maximum
(2011-2015), 4-6 x 10^22 Mx of flux is missing from SFT models that do not
include far-side data. We find that while He II 304 \AA data alone can be used
to create synchronic maps of photospheric magnetic field that resemble the
observations, it is insufficient to produce a complete picture without direct
magnetic observations from magnetographs.
