How to transfer external source journals both primary and secondary ledger?

Dear Experts,

Customer has one primary ledger and one secondary ledger. Also at secondary ledger journal conversion rules from primary ledger are disabled and all the journals need to come directly from sub-ledgers to both primary and secondary ledgers. This way any sub-ledger transaction journals are directly posted to both Primary and Secondary ledgers from SLA.

Currently business requirement is to transfer all of the external source (like POS, PeopleNet and so on) journals through SLA so that any account modifications need to be taken care using SLA rules. Once these journals are at SLA, it should post both in primary and secondary ledgers similar to any sub-ledger transaction journals.