This is all the only online help from Sage 

http://desktophelp.sage.co.uk/sage200/professional/Content/NL/Consolidating_Foreign_Currency_Nominal_Ledgers.htm?Highlight=consolidation%20foreign%20exchange

You have probably already seen it.

personally have experienced issues with customers trying to do this, and they decided to give up and go back to excel!

I've always thought the idea behind currency consolidation was wrong, as (roughly) it posts the movement on the subsidiary account converted at the current exchange rate. So if there's no movement on the account, nothing is posted.

My view is that - for balance sheet accounts at least - it should post the difference between the last consolidation value (in parent company currency) and the current consolidation value (again in parent company currency).  So if the balance on an account hasn't changed, but the exchange rate has, the parent company account balance will change to reflect this.

I did actually do bespoke for this a long time ago, but haven't looked at it for years!