I only deal with companies that 'pay' subcontracTors and so only book such invoices into the purchase ledger. Amongst the many many invoices that I receive however (lots of subbies!).....very very few contain such a calculation.
I might be wrong, but it is fairly irrelevant and can also cause incorrect postings in the clients accounts as the total needs to be booked and then the CIS deducted (by way of credit note to CIS Tax liability account).
I expect that the total is booked in the subbies accounts with the 'underpayment' booked as a debit to the tax liability account.
If you have a professional invoice already, would it not suffice to insert some text stating that 'xyz is registered for CIS...please deduct CIS Tax at the appropriate rate'?