Finally, I did it. I used potato starch, but corn starch will be similar.
Add starch gradually into hot water, 208F to be exact. Stir and dissolve. Add starch until mixture is very thick and do not dissolve starch powder anymore. The ratio will be between 5:1 to 5:2 by volume of water to starch.
The cup I use is 3 inch diameter, flexible plastic cup from fast food joints. I put a 1" PVC tube for water in the middle of the cup, for the tunnel for my cock. Microwave the cup and tube for roughly 30 sec, so that the starch boils over a little bit. The tube have to be a somewhat smaller than your cock, but not too small.
Wait for the starch to cool down. You can withdraw the PVC tube by twisting it while pulling. The starch will glue to the tube but still you can pull it out and leave a tunnel in it. That can only means success.
You have to make a small hole at the bottom of the cup to let the air out when you pump. The starch will block the pump from time to time and became very noise. You can make a bigger hold and worry about reusing the cup next time.
When you charge fast, there's a lot of resistance. When you pull out fast, there's a lot of suction, but the starch stays in place, ready for your next charge. You can do it fast with very pleasant feeling, no hurting. When ;you move in and out slowly, it's like a blow job.
The best is, you can do it hand free. Next time I'll see how to mount it on the table top.
No more jelly and grass jelly because they melt.
This is the picture of the fleshlight I made, AFTER I had sex with it. You can see my cum in it. Sorry about that.