We are using Multidimension group called Letter of Credit then adding LC codes within this group.
Whenever you issue an L/C just create it and make the necessary JV's for any transaction you do.
In my openion in case of Payable; create a payable class which points to an L/C account which is a group code account, so when you open an L/C just create an L/C code and point your JV's to it. Then when you receive a vendor invoice the system will credit L/C account then L/C code...
You can use AA instead of multidimension.