Hmm, that does sound tricky.
As an alternative, would it be possible to bypass this by simply considering the opponent as having played a card?
Subcontractors (Common)
Cost: 0
If enemy's last card had a Bricks cost, steal Bricks equal to 1/4 it's cost.
Mana Drain (Common)
Cost: 0
If enemy's last card had a Gems cost, steal Gems equal to 1/4 it's cost.
Deserters (Common)
Cost: 0
If enemy's last card had a Recruits cost, steal Recruits equal to 1/4 it's cost.
Glorious Appearing (Rare)
Cost: 15/15/15
Replace hand with Gift from the Heavens, Fairy, Heavenly Warrior, Paladin, Cathedral, Zealot, Seraphim, Angel
Fatalism (Rare)
Cost: 15/15/15
Tower -20, Enemy Tower -20
If this would cause you to lose, Enemy Tower -30.
Disarmament (Rare)
Cost: 10/10/10
Converts all resources in play into bricks.
Discards all cards in play with a non-brick cost, replaces them with random common building cards.
Madness (Rare)
Cost: 0
Stock -10
Enemy Stock -10
Replaces all cards in game with random non-common cards.
Megalomania (Rare)
Cost: 20/20/20
Swift
Facilities +5
Stock +50
Tower = 1
Wall = 0
Premature Conclusion (Rare)
Cost: 30/30/30
Tower -30
Round = 249