Another option - hire high ranked member to post ANN thread. But you need to find member with good reputation.
For me, if you do something like this I'd see you as trying to 'fake' your reputation. It's better if you use your own account, Copper member is made for this purpose. Who post your ANN & Bounty thread doesn't bring any credibility if your project is not good. You should focus on your project more than deciding how you made your ANN & bounty thread.