AFAIK under JAA if your non typed then you cannot log the time at all. Further, if for example you did have a type rating BUT the operator was NOT approved on the AOC or under JAR-OPS to operate the aircraft multi crew then you can't log the time either.
If it was me I would still hitch the ride and soak up all the experience and add a column to my logbook for safety pilot hours. Make sure that the hours do not add into your total flying hours. Then when applying for any jobs at a later date you can mention the safety pilot hours in your covering letter.
Have a read of LASORS - Section A Appendix B under Recording of Pilot Function and in particular the notes that refer to Co-pilot time. There are good references to the ANO and also to the Certificate of Airworthiness.
This has long been an issue for aircraft like the smaller Kingairs which in the UK are often certified as single pilot yet for insurance purposes a safety pilot is carried.