Do you mean RES, or do you mean i-VES? RES is factory only, i-VES is dealer installed only. Both are Honda authorized accessories.
The factory RES isn't designed to be a dealer install item.
Perhaps you could buy the components separately, and perhaps the wiring is all there to plug it all in, but you'd spend WAY too much money to make all that happen. I can only imagine how much they want just for the RES head unit, let alone the DVD player. You'd be into the many thousands of dollars buying this stuff after the fact and trying to get it installed.
So, the answer to RES is to look at aftermarket. The same $1500 that the RES would have cost up front can buy you quite a nice third-party DVD system installed, from what I can tell from the many stories folks here have shared with us.
If you really want a DVD system, shop carefully and be sure to come here and ask plenty of questions. Go to the audio/video forum and spend time looking around, and ask specific questions until you're happy with your level of knowledge. Whatever you do, get the right system for you. Don't underpay, don't overpay.