Don't know how to handle this, so please help...

I have booked 7 nights in Jun 05 at one of the London Marriott's (confirmed)

However, I won't need all 7 nights, but would prefer 2 rooms for 3 nights (ie, I lose one night but I don;t care).

Called MR and said they can't do that for me......called the hotel manager..they referred me to MR.

Any suggestions or ideas on how to use it for 2 rooms/3 nights?