Reverse directors wages for year?

I have just taken over a new client, seems previous advisors have allowed the 2 directors (who are also shareholders) to continue paying themselves normal hourly wages with no obvious reason (dirs wages are at around £30k each a year, which is way in excess of standard £624 monthly amount for directors on salary & divs mix).

Assuming there will be sufficient profits when accounts are prepared - is there any reason why we could not reverse both directors wages from April '12 to date and pay them the £624 per month instead (purely from payroll perspective) - we don't think they are on RTI yet so HMRC have no knowledge of what has been paid in the year to date except the PAYE figures. PAYE has been paid up to date, with around £20k of it relating to the directors! - so therefore if we could reverse the wages to date they would get the £20k refunded.

Is this possible? Has anyone else done this before?

My only reservation is that it will raise suspicion with HMRC regarding the potential £20k refund - is this likely?

Thanks in advance for any replies.

(PS am only interested in this from a PAYE/payroll perspective - i realise that there will be other considerations when we come to prepare the annual accounts)