How to return response without waiting for downstream in spring integration DSL

Question

I've got Integration flow which expose endpoint (inboundGateway), proceed transaction (some transformation) and send to downstream (outboundGateway). How can I return response to upstream directly after received transaction without waiting for transformation and result from downstram? Response like 200 OK (some kind of acknowledge)

public IntegrationFlows
   .from(Http.inboundGateway("test").errorChannel("failures").get())
   .handle(Http.outboundGateway("http://example.com/test").httpMethod(HttpMethod.POST).expectedResponseType(String.class).get())

Above code gets transaction, then sends to downstream and finally return response from downstream to upstream. How can I return acknowledge to upstream and then skip response from downstream?