I understand the difficulties in losing an encryption key. Key management is a tricky topic. Our goal with LiteSpeed is to provide the highest-level of security for encrypted backups. Unfortunately, storing the encryption keys in the repository is not something on the roadmap at this time. You may want to look at third party key management solutions that may be able to assist you in tracking keys in a secure manner. Googling "sql server encryption key management" brought up some results worth investigating.
Thanks.