There is nothing you can do regarding alternate if you want to have a realistic vertical profile computation (descent to destination) and trip estimates on time/distance to go etc.
Something I have never used but was discussing with another friend who has a 296 was how to set up a virtual ILS for a specific runway.
You set a final waypoint at the aiming point of the runway (where the glideslope antena would be).
Then you set another waypoint (initial) in the point where you should start your descent. Account for 330ft per nm of track to find out how far you want it.
Make sure you have no terrain below.
Roll laterally the initial point so that that the track connecting is the track of the runway.
Set the Vertical navigation profile of the 296 to be 0ft at 0nm of the destination.
When you taxi onto the runway at the touchdown area record the GPS altitude at that point. and also move precisely the waypoint to the exact location you are, provided you are on the runway centereline.
Then go back and edit the final (touchdown) waypoint's AMSL altitude to the one you see at the GPS.
Save the above two connected points as a flight plan that you can call up in the future.
With this you can simulate an ILS via loading up the FPL and following it via the page showing the miniature aircraft panel and the two bars in the HSI.
Things you must
not 
do with the above :
Never rely on it for actual ILS simulation in IMC.
GPS and units like the the 296 specifically are
inacurate both laterally and vertically for guidance towards such a precise 3D point in space.
Just do it for fun some day with nice weather out of curiosity to see how reliable it could be and how far down the virtual ILS you can keep the needles centered. Do not do it without someone else looking outside the window for traffic and terrain !
Also remember : the mini panel instruments show you
groundspeed in the ASI ,
track being flown in the HSI and GPS altitude in the Altimeter, not Indicated Air Speed, Heading and barometric altitude.
You'll find that AMSL baro. altitude may deviate as far 200~400 ft from the GPS one.