Thanks for the post. When you do get the time, send me a PM.
I'll just put out in the open - who knows - it may generate a discussion. And forgive the "stream of consciousness" style of my post.
On the regs:
61.63(b) - Self explanatory. A note on endorsements though:
Since he isn’t a student pilot, he does not need the solo endorsements that pertain to student pilots per
§ 61.87, 61.93, 61.95, and 61.131. To solo, the only endorsements needed is per
§ 61.31(d)(3) – “To act as PIC in an aircraft in solo operations when the pilot does not hold an appropriate category/class rating.”
Additional endorsements may be required from
§ 61.31 if the airplane is a tailwheel, complex, or high performance aircraft. Be advised though, you may put any limitations on the solo endorsement you see fit.
The endorsement required for the practical test will be different than a conventional applicant as well. This endorsement is from
§ 61.63(b).
There must also be an endorsement from
§ 61.39 stating the applicant has received and logged training time within 60 days of the practical test.
Your student will not be required to take a knowledge test per
§ 61.63(b)(5).
All the above-mentioned endorsements may be found in AC 61-65E.
61.109 (a) - he'll need a min of 20 hours with and 10 solo. From there on out anytime if it says "airplane," he needs it.
Knowledge: Don't assume he knows it all because he already has a certificate. He probably knows a great deal already which should make your ground sessions easy compared to a new student pilot, but the difficulty comes because he will have gaps in his knowledge that you don't know about. As an example, on the surface he might have a good understanding of aerodynamics, but you need to probe a little deeper as it pertains to a fixed-wing to discover the gaps. His understanding of a stall in helicopters is very different than yours (ask him about retreating blade stall to find out why

). While he may have a superior understanding of class G airspace, he may or may not be very well versed in busier airspace, and probably lacks certain regulatory knowledge pertaining to speed limits, O2 use, etc. This list goes on and on. It will be a fine line between inadvertently talking down to him vs. not teaching him enough.
Flying - he'll probably never want to let go of the controls. He
may be familiar with trim, but in a different way than in a fixed wing. His view of the pitch/power relationship may or may not be different than yours. He will not be used to landing at speeds above 20 knots. He should be fantastic at keeping an eye out for emergency landing areas, but keep in mind he'll be looking much closer in and may not realize he needs more than just a clearing to land in

. He should be good at maintaining airspeed and altitude via external cues - highly doubtful that he'd be glued to the instruments. He should be good at all the ground reference maneuvers already. Where student pilots may have a tendency to over control, he might have a tendency to under control.
That's about all I can think of right now. Hope it helps! If you have any other questions feel free to ask.