PhD student no CSI :(

[mstudentnocsi]

Hello,

My circumstances:
Nov 2006 - Jan 2010: PhD student with no CSI
Feb 2010 - now: Worker with WRS
British Citizenship application made on the 8th May 2014
5 year period May 2009 - May 2014

My application is still being considered, I received a letter to provide following documents:
1. Evidence of exercising treaty rights during 5 years
2. Alternative evidence or residence
3. WRS registration
4. CSI for the period of PhD studies

The last point made me jump as I don't have the required CSI - I never needed it until now.
During my PhD I received a scholarship (non-taxable) and did some laboratory work for the University but without WRS.
I started self-employment in May 2008 but worked only for a month (I have a single HM Revenue statement).
I got my blue registration certificate in Feb 2011 - this might be crucial.

So my question is - what is the best way of replying to the HO in my situation which can be summarised as follows:
Phd student without CSI and working occasionally for the University without the WRS but self-employed for a part of the time?

I would really appreciate your advice,

Thanks