We have been doing some experimenting with how to tweak Isla Dorada as a two player game. Technically it requires three to six players and has worked brilliantly when we have had enough people to hand to reach those numbers. It does work with two to some extent but loses out the twists and turns imposed by more people trying to bid for the right to lead the expedition and pulling in several incompatible directions.
The most recent attempt involved two altered mechanics. One was to adjust the bidding process so that the current expedition leader states how many points it will take to chose the path and the other player can either pay this and take the lead or chose to pass (either for strategic reasons or through paucity of cards). I picked this idea up from the BoardGameGeek site in a discussion on 2 player variants.
The other twist was to use a die to create a random element. If the result of a D3 roll (half the face value from a six-sided die, rounded up) exceeds the stated cost, then control of the expedition passes to the other player but the path is determined with another roll to randomly pick from the immediately surrounding choices. My theory was that this is a low enough threshold that players can often afford to set the bid rate high enough to exclude the random choice but that, given the normal economy of cards, it will come into play from time to time so that, as with the normal game and a decent complement of players, there are areas it is wise to give a wide berth to unless you are confident of a strong enough hand to get in and out without an unwanted detour.
How did it work out? Moderate success. I liked it but Jane took against it. I shall either have to persuade her to try again and give it a better crack or start work on a solo-player variant!