The advertising sort of worked on me this week. I already had psychopath test, and because I already have an audible account and maybe being in the UK it would have been a moot point . However I did add Michael Shermer's book to my wishlist and will be listening to that after my cuurent one.
I think that it would be reasonable for Steve to advertise his lecture series regularly and maybe more often. Maybe once every 3 shows or whenever there is a gap in people requesting advertising spots. Or really as often as you like because it is your podcast.
Maybe possible advertisers like New scientist, Omni and the like would be good candidates. Fortean times even, in a "This is what people believe" way of selling it.
There are the companies that manufacture or just sell study aids, and science equipment. Maybe the advertisers can offer a discount at whatever store online sale.
Just some suggestions.