entertaining Retention Money as per client specification

I have some problem in entertaining Retention Money as per client specification.

Senerio is client want to calculate retention money in running incoming invoice. Now I tried to do this through instalment payment customisation. It is working fine but only problem client want retention amount in seperate Gl and not in vender recon. account. If you use Special Gl indicator, it will post all the instalment in alternate account, whereas we want only Retention Amount which is to be paid after one year for example.

This is the whole senerio, if you any other information in order to help, please specify.

Thanks for the time

Answer:
try Define Alternative Reconciliation Accounts and enable recon account ready for input in GL master.