Sorry for reviving the old thread. Thought I'd share the outcome if/when someone runs into the similar issue.

If two passengers with the same names travel in the same cabin, splitting the PNR will NOT help to make OLCI functional. The only way to make OLCI work is, indeed, to enter slightly modified first name (John --> JohnN). I highly recommend doing this sooner rather than later. It took the outstation staff in VIE 45 minutes to check us in. And only after the supervisor arrived.

Hope this helps and thanks for all your efforts!