Hi P K,
This could be done in multiple ways.
The blog @ http://scn.sap.com/community/erp/hcm/employee-self-service/blog/2013/05/06/making-ess-personal-profile-read-only-dynamically could give you some hints.
Also from the blog @ http://scn.sap.com/community/erp/hcm/employee-self-service/blog/2012/06/13/summary-of-configuration-options-in-ess-personal-information-scenario
you can explore Layer 2: PA UI Conversion Layer.
You could add custom logic to make all the fields from IT0009 as read only when it is onbehalf scenario (hint onbehalf sy-uname <> pernr being edited)
Also do read through http://scn.sap.com/community/erp/hcm/employee-self-service/blog/2012/05/29/exciting-enhacements-to-ess-personal-information-scenario-in-enhancement-pack-6
Hope this helps you to come up with a solution.
With regards,
Sahir.