Stonemason has similar, if not more, synergy with Spice Merchant in this case. Overpay to get 2 Spice Merchants and a Stonemason, and you can thin your deck of Estates *and* Coppers while getting some early +Buy / nonterminal draw to set up your engine. It's slower than other trashing methods, but there have been games where Spice Merchant is the only source of +Buy and I feel this would help.