Using my definition of API virtualization the answer is yes. This is done via null target proxies or node.js target proxies for more complex needs.
Here are some links that help explain routes and targets, including null targets.
http://docs.apigee.com/api-services/content/understanding-routes
https://docs.apigee.com/api-services/reference/api-proxy-configuration-reference
https://community.apigee.com/questions/10603/how-to-send-response-from-proxy-end-point-without.html