Asynchronous web service Calling in Flow service.

How to create/call Asynchronous web service in a flow service?

For Example:

There are 5 steps in flow service.
First Step is Invoke web service, that inserts the data into database and it takes 10 min to complete.
remaining 4 steps should not wait until the completion of web service.
Without waiting for reply, next flow steps should complete the execution.

Please share ur suggestions… Thank u

If you think remaining four steps can be executed without waiting for web service call, they are independant of each other. Move those 4 services first, and invoke web service call at last as they are independant.