Thanks Palal, you summed up in a couple of lines what I thought might be the case. Maybe I could book a refundable rate at the Holiday Inn where I am going and get them to issue me an invitation. Perhaps I might anyway spend a night of two there if the next Accelerate promotion is worth participating in.
I thought it might be interesting and useful for other posters to have a general Russian visa thread here, as there is not a huge amount of traffic about this on Flyertalk.