Make no mistake: 91.409(a)(1) is unambiguous. Only IA's and Repair Stations can perform (*not supervise!) an Annual Inspection. I'm not going to argue with the FAA on this one.
That's why it's important to clarify the description "owner-assisted" Annual.
As you probably know, Appendix A to Part 43 (c) has a lengthy list of preventative maintenance tasks the owner (that holds at least a pilot certificate) is permitted to accomplish. Many of these tasks can be performed simultaneously with an Annual inspection. FAA legal interpretations have explained owners are allowed to perform tasks incidental to the Annual inspection (for example: removing inspection panels or cleaning spark plugs.) What is absolutely critical is only the IA is qualified to inspect an item and make the determination of its airworthiness.
What this means in practical terms is you shouldn't have to pay me to grease your wheel bearings or safety your oil filter back on. That's where the cost savings (in labor) occur during an owner-assisted Annual.
We work together as a team. I can perform a competent and thorough inspection while you help out with the ancillary functions of aircraft maintenance.
Of course, we can discuss the specific tasks we're expecting the other to perform prior to work so there's no surprises once we start your Annual (and I'm always very happy to teach interested owners tips on how make to maintaining their aircraft easier!)
*Far too many shops engage in the unfortunate practice of having an A&P perform a 100 hr Inspection and then pass the logbook over to an IA to check the AD's and then sign off an Annual Inspection on the same date without ever having looked at the plane itself. This is not just a bad practice, it is a flagrant violation of the FAR's and a disregard for their responsibilities and privileges. Steer clear of places engaging in this activity.