You've answered your question in the question. There is a whole area called "manufactured spending" which has solving the problem you describe as its goal.
The game is always evolving as existing methods get shut down and occasionally new methods are discovered or become available.
A few years ago, for example, I would go to my local Fred Meyer, buy Visa gift cards, then take those gift cards to Walmart to buy a money order, then go to my bank and deposit the money order. I could then pay back the credit card with my bank account.
It basically was a moderate hassle way to move money in a circle to make it look like you were spending without actually spending. Depending on the particulars, you could do the above process at a cost of about 1% of the money you were moving in a circle. Which was well worth it to get the sign up bonuses.
The Walmart loop above is in the process of getting shut down, by the way, so it may or may not work in your area now.
But there are always ways. If you're interested, just google manufactured spending, pick a forum, and start reading. They use lots of acronyms and code words in those forums, but if you read enough and google enough you can pick up the lingo. I think two of the best forums are on flyertalk and reddit.
