Excess NI

Doing Self assessment for client for 2010/11. He retired half way through the year and set up as a self-employed sole trader. His class 1 NI in the first half of the year and Class 4, as assessed, together exceed the maximum by some £1700. Is it right that there is no way to self assess the true amount of Class 4 payable but instead I have to assess the nominal full Class 4,and client has to pay it before 31 January 2012, and on 1 February he can submit a claim (CA5610) for a  refund? Or have I missed something?

Would very much appreciate confirmation or otherwise. If I'm right, I'm Just wondering how I'm going to explain this to client. . .