You can not buy a place, if you did run under someone else bib, you and them are banned from all the London marathon groups events.
you can buy a travel package, and you could raise money for charity - usually they rerelease places as people drop out nearer the time for far less sponsorship.
there is always the volunteers ballot, we volunteered at the finish line and for us 120 volunteers we got 3 spaces, we did a draw but I suppose you could bribe the lead if you volunteer to get the place.
the other option is enter an address which is on the London marathon route, as you have improved odds, nothing is sent out so you collect everything at the expo, I’m sure some people do this year on year