I think a current colleague / supervisor is a lot more important than people like to imagine. I also think that the excuse of lacking the confidence to ask your manager really doesn't sit well. If you are a consultant on a shifting team or in a family business, fine - it obviously has a problem or a conflict. The job security thing.... I remain entirely unconvinced. Most managers would be way happier than you may well imagine to provide support and recommendations to you furthering your career. They have been around long enough to expect people to move on, and treating them with dignity and respect through things moves you up in their estimations. Sure, it is an issue in the near future, but they also feel quite proud that they were involved in you aiming for such aspirations.
Just ask, and allow them enough time it isn't a stress to complete the recommendations.