In trying to get more people involved in my crypto currency prediction and stats system
https://bitbank.nz on the marketing side I created a referral program which helped my normal customers be a bit more sharing
but pro marketers eg ones on freelancer want more stability than that and a more well defined task than being an affiliate, which is fair enough, they work for money and Im happy to take on the risk of my site not converting people to customers.
It's hard however to invest in people upfront when they don't know where to start
It's good to outsource if there's a literal to the letter description or if it's something outside your forte, design and marketing I in my case,
I have had a good experience running design contests on 99 designs or using their small design touch-up service. I ran a contest to get a logo designed for a game I made which paid off (http://wordsmashing.com) it requires active management otherwise the designs drift toward something unwanted, id say run a blind contest too because designers copy each other and end up with less variety otherwise.
I'd feel bad not paying proper rates but if it's something on the verge of automation you could try mechanical Turk.
Let me know what you find! the type of sporadic tasks I would have are things requiring non trivial domain knowledge and self direction, things like article marketing or link building which can be hard to find someone trustworthy and self directed on a party time basis