Create a delegate private key in your browser, approve USDC once, and register the derived Safe as your on-chain delegate. After that you can use the Builder SDK in Delegated + Gasless mode: trades are signed by the delegate and submitted as sponsored ERC-4337 UserOperations via a Pimlico-compatible bundler (Ostium provides a default sponsor URL).
The Builder SDK overview covers requirements, the delegate model, gasless trading via Pimlico, and full code examples. We recommend reading it before you integrate.