Service tax (India) - input credit change

There has been change in the Law for availment of service tax input credit on the similar lines with Cenvat Credit i.e. Now onwards Service tax credit will be available at the time of "Purchase Invoice Posting" and not at the time of "payment to Vendor".
This is a major change for version < Nav 5 , 2009 since no support/hot fix will be available by Microsoft for these versions.

Has anybody work on this as to how to map this? or is this will be a major customisation??

Regards,

Prashant