CIS for non resident trader

Advice would be appreciated on obtaining CIS registration for a construction based outside the UK. My client is based in the Republic of Ireland. It has won a short term construction contract with a value of around £1m in the UK. This is its first UK contract. Its customer would appear to be deemed to be a contractor for the purposes of CIS. Accordingly my client would need to show that it is entitled to gross payment, or it would suffer a considerable and unaffordable cash flow disadvantage. The Irish company has a track record of full tax compliance in Ireland, but has had no previous tax responsibilities in the UK. Any advice as to how best deal with this would be much appreciated.