I suppose a warning is in order, which you probably already know, that complete data loss is a high probability. Maybe you could re-image the drive after even if you do loose your data.
That being said, here is a site that goes through some options. One of which, using a Hex Editor, is suppose to restore the drive to basic without data loss. There are also some software options mentioned. But I have not tried and cannot verify any of these processes.
Convert a dynamic disk to basic disk by three ways and software to change/revert to Basic Disk.