For now, let's think of it as eHalcyon's explanation. It's closest to the original spirit of the thing. The big obstacle, as I see it, is getting a large enough number of useful cards in the deck that some will be useful even if the best are discarded. Nomad camp is probably a useful tool, considering the fact that it can easily dodge the spy's strikes. For thought experiment purposes, I plan to identify the course of events that would befall a pure Big Money board.
Assuming the worst possible split would give us 2/5, but this can naturally be improved with Baker in kingdom. It doesn't complicate things excessively, and most of us will use a Baker anyway, so let's grant that the player opens double-silver, spending the coin token in the process. The silvers fall to the 6th slot and 12th slot, and are removed by the spy. Turn 3 is 2 coppers, 3 estates, and turn 4 is all copper. Therefore, pure BM player purchases a single silver. On turn 5, there are 13 cards in the deck. If the spy knocks out silvers on cards 6 and 12, that leaves 1 silver guarenteed in this shuffle. turns 5 and 6 once more mirror the opening splits, and a 4th silver is purchased. Then the reshuffle occurs, with the first silver the BM player actually has in hand. Let's pair this with three coppers and a single estate. At this point, you can see the sort of problems any player would have.
I wonder, though, what impact it would have if the BM player didn't spend the coin token early. That would allow the BM player to score a Gold on any 5-value hand, which might accelerate things. Of course, that Gold would likely see little use given the powers of the spy. Is it an option worth considering for the BM player?