Ive been trying to game yelp for the last year....here are some tips, you need need different ips with the accounts created in the same country or better yet state as the company, even if you post a review with the account it WILL stay up for a week or 2 BUT if you leave the account inactive your review will be filtered and will accomplish nothing...
its better to have someone build up the accounts not just with a profile and picture BUT, they need friends, they need previous reviews
TIP: Dont make the first review on your new yelp account on a business you wish to promote, make like 30 reviews first before you give reviews on any business you need then start requesting friends and once you have a decent amount than start posting reviews on businesses you need.
Keep the review believable use some 4 and 5 stars as well as at least a good paragraph in the review...
I do this for NYC biz's and im in the area if you need help pm me