It's not a different approach. The idea of giving a programmer 50% ownership of a pie in the sky idea instead of a salary is 40 years old. So is the idea of convincing some sales genius to work for you for maybe a payday some day in the future.
You're not going to get someone to give you money to let them sell your ad space. Even I'm not that good of a salesperson, and I sold to salespeople for years. I suggest you remove that idea right out off the table.
Here's my short answer. You need to suck it up buttercup, and do the marketing yourself. I know you don't want that answer, but it is the answer. If you don't do that, you will not likely be successful.
I say that based on my experience. I had a website that generated a ton of traffic that needed to be sold. I tried everything - and the only thing that worked was my actually doing the sales. Now, somehow, I'm an accomplished salesperson. And I'm beholden to no one. In short - I've tried a whole bunch of things that involved someone else doing the sales/marketing and I always ended up unhappy. If you want the tip of the iceberg on your problem, what if you give someone 50% and they don't do the job you want..then the website takes off some other way and they're in for 50%. Lots of other bad scenarios can happen, and I've enjoyed them all. There is no case I've seen where the scenario you're presenting ends up with you happy.
I have experience from the other side as well. I have a friend who had an excellent website. They offered me 1/3 of their site in exchange for selling their ad space and helping grow the site (since, see above, I somehow ended up being successful in sales, despite the fact that I'm a tech). I declined, I simply don't have the time or interest in taking a startup project from someone else and making it take off. In short, I don't want 50% of nothing.
Funny story (funny ironic), a few years ago they came back and asked me to sell their traffic. NOW they had huge traffic and were successful. So now I said sure, would love to do it for a 1/3. They responded that they weren't going to give me any ownership, just a commission. Again, that was unattractive because I already have other stuff I do.
And the moral of that story is, you should appreciate that the way this will be percieved is that you're offering 50% of nothing AND you want someone to pay you for that.
And it's not sales or marketing. It's no harder than pick up the phone, call a potential advertiser, and ask them if they're interested in advertising. It's not the bogey man here, there's nothing to know. All you have to do is pick up the phone.......