After trying many different tactics (using a bird, a pen, etc) the best way by far was to ride into the swamp on a big dino that the titanoboa will ignore (i used an allosaur), kill all distractions around the boa that I wanted to tame (phiomias, trikes, etc.) and then drop fertilized eggs from my own inventory directly on the boa.

If for some reason the boa attacks you, forget it and find another since you won't be able to tame it (won't eat the eggs).

You can use honey to attract the boa near your egg if it went away (remember that dismounting without ghillie & repellant will probably cause the boa tobattack you).

More Titanoboa Taming & KO Tips