Yes you can but there are only 2 ways.
Either via the IRClone method (
http://www.irclone.com) or by using a One For All/Radio Shack model that supports advanced codes (
[Link: hifi-remote.com] You may need the JP1 protocol to get some of these codes though. JP1 is also discussed at this site.) The OFA/RS method is cheaper but IRClone brings some other neat tricks to the table. (IRClone shipping has apparently been delayed due to a parts issue. But they are saying they'll be ready to go again sometime in July.)
Your 2803 supports many advanced remote controlled functions that aren't on your factory remote. Features such as panel dimmer, video select function, direct volume jumps to 0,-20,-40, individual tuner presets and direct switching to surround modes (such as DPL II Music or Mono Movie, without toggling thru all of the other modes.) Many of these have been obtained using the OFA/RS method. But once someone who uses IRClone has them, they are easily traded between users.