Start networking and lining up other prospective jobs. When you have some strong leads, you approach your employer about renegotiating that part of your employ

Start networking and lining up other prospective jobs. When you have some strong leads, you approach your employer about renegotiating that part of your employment contract. Don't threaten to quit or hold those leads over your employer's head. Express that some of your colleagues with other companies are explicitly allowed to own all of their projects developed during their own time. If that fails, follow through on those leads. Don't work on any personal projects until you have officially left your current job.