Anybody extended factory 496 ho stainless risers to Introduce water at the tip to avoid reversion? Thinking I could just add a piece of stainless Pipe and extend the exhaust right to the tip?

Yes. I have 3" stainless welded to my risers so the water mixes about an inch from the tip. Pretty much a makeshift dry system, it will make it quite a bit louder tho

this is what your looking to do

Did you just weld a piece for the exhaust, and still slide the long rubber sleeve clear to the riser allowing water to exit between the two?

I am not sure about the 496 risers, but on every boat that I have had I extended the inner and outer pipes to within 1/2" of the tips and used a short rubber coupler. Works well

This is correct. I temporarily mounted the risers, and tacked the stainless extensions in place perfectly lined up with the tip. I did this so the extension did not make any contact with the exhaust hose. Then I removed them and did the final weld. Water exits riser in normal location but doesn't mix with exhaust until the tip. Looking at it on the boat complete it looks exactly the same as it did before the extensions

Not to be a stick in the mud but those extended pipes are gonna get hot. When water comes out of the top/end of the riser it hits the original inner tube's bell flair and it splatters water up and around the flair cooling and then being carried by the exhaust gasses before it hits the rubber exhaust hose. Extending inner tubes like above, the water will come out of the riser and just run down and around (to the bottom of) the outside tube. Probably all happening within a couple inches of where the water exits the riser. If I were to do it at all I would leave the bell flair and put the extended tube inside of it but only for a couple inches at most. Something that long should be water jacketed.
Not sure why you would need to extend them anyway. I use them on almost every boat I 've owned. Here they are on my race boat with Kiekhaefer 482ci off shore race motors. I had to have a motorcycle shop make them taller because how high the exits were but nothing for reversion.

I did it for the sole purpose of getting a little more bark out of my 496's. This will be my third season with them like this and I've had zero issues. My 5" tips have internal flaps and they have not been affected by any excess heat, I understand what you are saying tho, I thought the same while doing it, that's why I made sure the extension didn't touch the exhaust hose at any point

They will be fine as long as the extensions don't touch the outer rubber hose. I've ran extended risers like above for 20 yrs on different setups. The amount of water exiting the riser especially at rpm cools the extensions fine.