I'm going to get downvoted for this, but make some fake content. Projects users can bid on, but will never win. If real projects get put up, manually try to get developers interested in bidding on it and into your system.
In reddit's case they were providing real content, just created by them. In this case the content is completely fake.
I also think this would be harmful to the business. I have very few interactions with a service before I make a judgement on them, if most of my interactions go nowhere (as would be the case if they are fake) I would stop using the service.
However if the service was just slow I would be likely to still use it, just check it less frequently.
Of course one viable way of adding content would be to repost content from other sites - with suitable indications of course.
Having people waste time bidding on fake projects that have no chance of happening is not the same end product as a realistic site where projects are posted by real people and have a chance of happening.
Also I'll tell you from experience: Even if your product is 100% real people who lose their bids are going to think it is a fraud. If you site actually is a fraud you are just going to burn through all the early adopters extremely quickly. The strategy should be the opposite --- have the content be so good that early adopters feel like they've hit a goldmine.
OP should consult a lawyer about the relevant legal and licensing requirements for running a recruitment agency.