I also have an aluminum frame on my bow sprit which bolts to the front AKA brace. The only reason I have a bow sprit sticking out 15 inches in front of the bow is so I can get free air to the spinnaker, you might notice the mast on the TI is mounted very far forward, I think the AI is similar.
The mast topper is incredibly simple and requires no modification to the TI in any way. Looking at the first pic, this is a 1 1/2 x 1 ft brass drain pipe I bought at Home Depot, ( I think it's for utility sinks). I bought a 5/16 x 3 inch long stainless bolt and drilled through the center of the pipe, then installed a nut and lock nut on the bolt, then wrapped it with electrical tape. I then loosened the downhaul line at the bottom of the mast and wiggled the little web of fabric at the top of the sail out of it's notch. I slid the pipe over the end of the mast and slid the web over the bolt on one side. Optionally you can wrap electical tape over the mast to get the fit between the mast and the pipe a little better. You then tighted the downhaul line back up, and your done (nothing else to do). The bolt fits nicely into the notch at the top of the sail so the topper rotates with the sail.
The second picture is the mast topper. I took a 1 inch galvanized pipe 4 inches long and connected to a standard 1 inch T connector. I then double reduced (ie.. 1 inch to 3/4, then 3/4 to 1/2 standard pipe thread). I then slid a 1/2 inch dia rod about 3 ft long and mounted 1 ft from one end of the rod. I used mild steel rod and (it's not quite strong enough, it also rusts easily), If I ever do it again I will use stainless rod. With stainless rod you shouldn't need the guy cable brace over the top of the unit. I tapped both ends of the 1/2 inch rod and put in eye bolts. I then took some 3/8 threaded rod about 8 inches long and slid it into the 4 inch long 1 inch pipe. I filled some of the space around the 3/8 rod with PVC pipe (several diameters inside each other) to keep the threaded rod on center. I then put everything in my vice upside down with the threaded rod removed. I then filled the whole inside of the T connector inside with West Epoxy (any epoxy will work), then shoved the threaded rod back into the hole all the way to the bottom. I filed a couple notches into the 1/2 inch rod (under the epoxy) so it can't work loose. After everything set up I took a piece of 3/8 PP hose and slid it over the threaded rod (siliconed it onto the threaded rod). Now you slip the new mast topper into the top of the mast, then with a hack saw adjust the length of the 3/8 rod so the end of the rod is the contact point to the side of the 5/16 bolt inside the brass drain pipe, and there is a small gap between the end of the brass pipe and the flange of the T connector (much less friction when firling if you have a single point of contact in the center, the PP tubing prevents the threaded rod from cutting into the notch at the top of the mast), Actually if I ever need to do it again I will use just standard 3/8 aluminum rod (not threaded). The ring nearest to the T connector is where I clip the jib sail on. The other one midway out is no longer used. The spinnaker clips onto the end eye bolt (on the short end). The rear stay line clips to the long end of the mast topper, then back to the rear lifting padeye. The whole works took me about 2-3 hours to make, no special tools (just a hack saw and drill), everything was right off the shelf at Home Depot. The whole works can be put on or removed either in the water or on land (for low bridges). I'm sure something else could be machined up that looks way more nautical (expensive) using the same basic design concept.
The rear stay line is a simple 1/4 inch nylon rope (stretchy) that keeps the mast from pulling forward too hard, It's stretchy rope so everything is forgiving. The mast topper and stay line do not interfere with the natural flex and bending of the mast.
It's actually kind of funny, all the parts you see in the pictures I made in spring/summer 2010, and wrote about in great detail on how to construct this stuff in the posting Ultimate Tandem Island ( viewtopic.php?f=69&t=33720
I have way over 2000 miles on all this stuff now in all kinds of conditions (35mph winds, 4 ft waves, etc) and have had no issues at all, except the sails starting to look ratty and in need of replacement, time to break out the old sewing machine again.
Chances are that that AI bow would have folded with or without the jib, when he hit the sand bar.