CIS for last month of trade

Good morning.

I think I know the answer, but thought I'd check if you have any ideas;

Sole trader - builder. Sub-contractor.

He finished ST 31.03.2012 and went LTD from 01.04.2012 as he is expanding and now a Contractor. LTD will be reg for PAYE / CIS contractor.

But, in the last couple weeks of March, he had 2 sub contractors. He's never had before and this is the first time and last time in the ST.

Ok, so technically, we need to register as employer / contractor for the CIS to be done, for one month. Obviously late return as it's past 19.04. Ok.

But do we need to register for CIS and as Employer for just one month, then cancel it? Or do HMRC have a "one-off" form?

Many thanks for any suggestions.