Hi Sandra,
we had a similar requirement and also requirement for triggering automatic posting in In house cash area. we have achieved it through Z Table and User exit. In Z Table, we have defined default BAI code and code which should replace it for a combination of House Bank+Company Code+AcctID+Posting rule in SPRO setting + Posting rule which should replace SPRO + Keyword 1 from statement file+ Key word 2 from Statement file.
on execution of FF.5, an userexit will trigger, this userexit will check the table and if it will find an entry for perticular posting item, then it will overwriteSPRO posting rule by table maintained posting rule for same BAI CODE / BTC
this will be posted to diff. GL Account.
for eg.
Company code - 0001
House Bank - SBI01
Act ID - INR01
BTC / BAI COde - 155
posting rule (as per SPRO) - D910
posting rule (whichshould replace) - D900
Text 1 - PAYMENTECH
txt 2- TRANSFER
Acct identifier - +
TRANSACTION TYPE - SWIFT 940
now, whenn Bank statement processing will happen, user exit will be triggered and it will go to this table, search if bank statement file if for above companycode, huse bank, acct id is there and if yes, further checks will happen. and if text string and if transaction if Credit 
then posting rule D900 will be triggered. instead of D910 which you have maintained in SPRO - > EBS Configuration steps.
Hope this reply will be helpful to you.
Regards,
Jignesh
(kindly give some point if reply is helpful)