Private Number Plate Help - Transfers

Hi all, i needed a bit of advise regarding private plates.

I recently bought my R32 with a private plate, Previous owner wanted to keep his plate which is absolutely fine. I filled out the new keeper slip and everything log book went off to DVLA, Initially the previous owner filled in the V5 incorrectly and the logbook was sent back to us in the previous owners name still. Fast forward we resent off the logbook as normal and it has now come back in my name with the previous owners private registration.

Now as i have been waiting for so long i ideally wanted to go into my local DVLA office and just have my own private number plate put on without having to wait weeks on end.

The problem is i need to return the previous owners plate (I still have his cheque made payable to the DVLA to put the plate on retention)

What would be the quickest way for me to have my own private plate put on the car and still retain the previous owners private plate. That way atleast my number plate goes on and then i can deal with the previous owner and make him the guarantor for the previous private registration.

Any help is much appreciated.