Notify as many end users you can find that the auction is taking place, a short email or call would suffice, let them know there has been a lot of interest generated about the domain being up for grabs.
I have even seen google ppc ads that the domain sellers have set up, it actually is not a bad idea in some cases.
Unless the (potential) buyers know of sedo and use/refer to them you pretty much have to get as much visability for your domain as possible, by your own means.