In the end it comes down to choice. To accomodate a reasonable well modeled, animated figure in a cockpit, something else would need to go.
For a figure to look half-way reasonable, the poly count could be as much as an engineer's station, nav bench full of working gear or maybe wings and engines out the passenger or crew station views.
Although FSX is far and away better than the old FS9 for limits on models, nevertheless, there are limits. It isn't just the ability of a video card and memory or a processor to handle them.
For a believable figure of the type you suggest, the count could be maybe 40-50,000 polys out of a total budget of 150,000. Game figures are matched to their environment so lower budgets don't notice so much. You can't expect laser accurate modeling of controls and systems, gauges and controls and then introduce a CGI figure. At least not in anything bigger than a light single engine basic aeroplane.
Maybe in FS11.....