Setting Lead / Lag on a predecessor using CSOM

I want to set a Predecessor on Task 2 using CSOM code. The predecessor is "1FS + 10days" 

I am currently stuck as i can't find any way of setting "Lead time" using CSOM. 

This is page from MSDN on DraftTaskLink Class

http://msdn.microsoft.com/en-us/library/microsoft.projectserver.client.drafttasklink_di_pj14mref_members(v=office.15).aspx

On the other hand, it seems possible (not too sure though) through PSI

http://msdn.microsoft.com/en-us/library/websvcproject.projectdataset.dependencyrow_di_pj14mref_members(v=office.15).aspx

Is this a limitation of CSOM ? If so, is there a documentation which specifically mention this ? 

Hammad Arif EPM Advice Blog