Requirement to have different COS Account

Dear Experts,

We have a requirement to have a different COS account specific for free of charge deliveries. These deliveries use order type FD, item category KLN and this is specific only to free of charge. Please advise, based on these 2 specific criteria of Order Type and Item Category, can we set up different COS account. I am basically a FI consultant and tried to achieve this using Substitution rule. I was able to set up per-requisites in GGB1 but could not find GL account in Substitution arena. Please advised, detailed solutions for this.

Any help in this regard is much appreciated.

Thanks & Regards,

Ajay Kedia