Join in multisource enabled universe using IDT

Hi Gurus,

I have a requirement where I am using,

1. An SAP cube via JCO and

2. A Oracle DB connection

and creating a multi source enabled universe using the above 2 sources.

The common field on which I have to join these 2 sources is order number. However in the SAP cube the number is in a different format ie

for example in SAP the field is = 12345

in Oracle DB table it always has a prefix "CI" like = CI12345

but these 2 fields are one and the same field and the join has to be on these 2 fields.

But how can I join because the contents are different. How can I remove the leading 2 characters "CI' from Oracle table and make the join?

Please help me with this req.

Thank you