Typically, the sponsor provides some form of prize. Maybe it is an e-book to download, what ever.
They provide it to the Admin. The Admin cranks out the statistics to show who wins. They make an announcement. So maybe a new folder that nobody but the admin can create a new post, but others can respond to say Congratulations or what ever banter they want.
The Admin e-mails the coupon to the winners contact list.
One year the wife and I raised over $60,000 USD in products for the school to auction off for fundraising. The biggest item was probably $300. It took a lot of time so we only do around $1,500 a year now.
I don't claim to be an expert, but this is why I feel it works.
1. Vendors must be asked.
2. They want to feel they get some exposure for their product. But, sometimes they just want to get rid of last year's merchandise and write it off at full price under marketing.
3. They typically want proof it was actually given away, not just taken by the Admin.
So, email the vendors. Describe the audience. Describe the competition (they do tend to like competitions e.g. school auction) In this case, it is international recognition.
Create a folder to announce This Month's Prize. Put a photo of it.
When the prize is awarded, send a followup to the vendor showing the results.
You are probably thinking, when am I going to find the time for this? I don't blame you.
In clubs past, Microsoft would give away full versions of say Windows 7 Enterprise (I see you like that one). I once won a copy of SQL Server 2000 Enterprise with a significant user CAL for answering a question.
If a folder was added next to water cooler that listed Prizes and Awards, we would all probably be surprised how many people would peek to see what is going on.
I support several non-profit organizations. One is a aerospace education officer for a aux youth services sponsored by the USAF. Ask a teenager to shine military boots. Or, ask Starbucks for cards to hand out to the best shined boots. It is amazing what people will do for a reward, recognition or a ribbon.
I was at the GoPro Expo in Vail Colorado a couple of months ago. I could not believe the waivers people signed and the stunts they performed for a wrist band or tshirt. There must have been a 1,000 advertisement signs there. But, every sign that had a "prize" had a crowd.
If it were me, keeping the ads the same, but driving up network usage with something different like sponsored prizes. You probably have a much better idea about this site than I do.