You can't with 0x, at least not in the way you could at say Bitfinex or Binance. All of the assets remain in your personal Ethereum wallet until a trade is matched up.

That's the genius of the 0x protocol. The Relayers that LaunchKit lets you create are effectively just order books or other matching-engines that exist as a website or other service. They expose completed trades to the 0x smart contract, which atomically swaps the tokens of the trade. (Official 0x people can correct me here, I've done just a bit of research.) At no point does any organization other than you actually have control of your funds, nor can they receive them without giving you equivalent funds under the terms of the trade.

I've said before that the real use-cases for blockchains will be in doing stuff that nobody in their right mind would want to do because it's currently foolhardy. This is a good example. Giving money to a fly-by-night exchange is foolhardy - unless you don't have to give money to them. And that's what 0x enables: tradable assets without trust.