You can try putting another male skin in to create competition with the scent of another male. Or put in another male snake in first to scent up the tank and later on only your prospect male to do the job. Normally jealousy makes them go crazy.
Or you can mist the tank when both of them are together, it tend to stimulate them with a higher humid environment, just don't overdose it. You don't want to face with RI or any illness.
Another way is instead of 3 days on and 3 days off, give them longer breaks for 5 days off 3 days on. Adequate rest tend to keep them going better. Oh ya, remember to feed them according to your routine to ensure their health are maintain and have the energy to mate.
All these methods are practice by me on my stubborn virgin spider. He refused at first but I guess he is just figuring out how to do it. After a few rest and putting together, he finally knows how to do it, and been locked for 3 times so far. Crossing fingers that he is not shooting blanksPatient and keep trying is crucial and never give up ! All the best