What about feeding data from 2 mechanisms into 1 goal?
Make "fail no dares" beeminder do-less goal (0 per week) and 'bets' complice goal.
Feed number of intentions in 'bets' goal into beeminder.
Through 'beemind arbitrary things', feed number of completed bets with a multiplier of (-1).
If you get into 3 bets and finish all of them then you have 3 (+1)s as you add bets 3 (-1)s as you complete them.
You can also track intentions through 'beemind arbitrary things', I think. By using negative multiplier on bets themselves and positive multiplier on bet completions, you can even get away with do-more goal.
Well, in theory. I don't know if it would work, but it might:)
However, I'd also advise experimenting with beeminding number of pomodoros. Sometimes outcomes are just not your fault; beeminding number of pomodoros gets stuff going.