Emmanuel,
If you are ussing IDM 12.6 you can create an admin task and mark it as webservice enabled. Then you can create a policy express to call this task as a soap webservice call (using TEWS6 functionality). Then you asing this policy to execute on primary (entry of user record) completition task.
When first task is compleated the policy kicks off the secondone by webservice. Yuo can even send parameters to this task, if you want.
regards
Fernando