Then just scalp forex. Currency markets are open 24x5 I believe? It's been a while for me, but if memory serves, Hong Kong opens at 3am ET on Sunday, and markets are open until Friday at 5pm when US markets close.
Best way for american to trade in foreign markets is american depositary receipts, work well for investors, as well as for non-US companies. ADRs offer investors a convenient way to hold foreign stocks and also provide an opportunity to non-US companies to establish a US presence and even raise capital in the US stock markets.