He's one of those players whose value to the caps is much much higher than that on the market.
He has several assets going for him. Name brand, Star player, Sells tickets. He's good for 30 goals still and all that. However, consider this.
His age makes him really only suitable for a handful of teams who believe they can win the cup this year or next. Now, almost none of those teams will A) Have the assets that allow them to actually acquire him without crippling the team and making them not a contender and B) Have the cap space to make the deal in the first place.
So there will be some retention on any trade, as cap hits like that just don't move in today's NHL unless it's to a team that is rebuilding and has the cap space, but then why would they trade their best pieces and set back their rebuild for a guy past his prime?
So, you need to
1. Find the teams interested
2. Narrow those teams down to teams Ovi will waive his NTC for.
3. Find which of those teams have assets you think is fair value for a retained Ovi.
4. Work out a deal and hope for the best.
I think you find yourself in the same situation of the Kessel trade. Maybe there is one team that has that fit, but you won't get his true value because they hold all the chips.
Really the only way he is traded is not for full value, but if the Caps think moving on from him is the best bet and try to get some draft picks and a few top prospects out of a team. In this scenario, they are likely taking back a cap dump as well just to make the money work.
So trading Ovi is more than moving a player, it literally weakens the team. This means if he moves, the logical following after that is to go for a full rebuild as you've weakened your time full of stars in their primes or passing it.
I think looking at the big picture, the value of Jersey's, ticket sales, and guaranteed playoffs for the rest of his career is worth more than what his return is on the trade market. Therefore it's doubtful he is ever moved unless he is literally run out of town. If that happens, expect a much lower return than you think he would get.