I would think the best way to use Scheme in a Minion game (assuming you joined the Minion strategy, instead of trying to beat it), would be to place a single Minion on top of your deck and then all the rest of your schemes. If you get Minion-ed, you only lose a single Minion, which makes it more likely that one of your other Minions will be in the four-card hand. If you don't get Minion-ed, then you play all your schemes and then any Minions. Basically you give yourself the best chance of always starting with a Minion in hand--which is really the key to Minion decks.