Change Implementation for Spring Namespaces (exchange a bean)

I have a question about Spring Integration (or basically Spring in common): I use the a WebService Inbound Gateway in my Spring XML configuration:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<beans xmlns="http://ift.tt/GArMu6"
    xmlns:int-ws="http://ift.tt/1sWxcZy"
    xmlns:xsi="http://ift.tt/ra1lAU"
    xsi:schemaLocation="http://ift.tt/GArMu6  http://ift.tt/1jdM0fG
    http://ift.tt/1sWxcZy http://ift.tt/1F2oEGL" >

    <int-ws:inbound-gateway
    id="ws-in-gw-user"
    request-channel="in-user"
    reply-channel="out-user"
    mapped-request-headers="*"
    />
...
</beans>

When I use int-ws:inbound-gateway Tag, a SimpleWebServiceInboundGateway is created. Now I want to exchange this implemantation with a self written extension of this class. Any ideas how to do it?

Thanks