I got you email and got side tracked and forgot to answer. I forgot about it till I just saw this. Glad you got this posted.

NO! IT IS NOT SAFE.

I mangled my thumb on a jig similar to this. The saw blade will eventually launch of those cut offs at you. I will not post the photo because of the graphic content, but here is a link to the photo of my thumb taken in the ER. You do not want to go through this! So listen carefully.

http://www.kudzupatch.com/temp/mythumb1.jpg

Take what you have.
Add a strip underneath that will ride in the miter slot and get the fence out of the way.
Run the jig ALL THE WAY through the blade and cut it flush!!
You want the scrap/cutoff to fall on the table. NOT on the sled. The scrap resting on the jig will get you eventually!
I used a clamp like you are using and it works but I do recommend adding some toggle clamps.

After several alterations I am pretty well pleased with this one. So far I have had no problems and I have cut A LOT of scarfs on it. I am always looking for ways to make it safer and I am sure there is something that could be done. But so far I haven't seen anything.