This isn't really a technique. Just a how-to guide on how to make a home-made fleshlight. I've done it and it really works, PLUS it's a lot cheaper than the real thing.
1. Put 100g of starch in a tall glass or ceramic cup
2. Add 100ml of water and mix thoroughly, then add a further 100ml of water and mix thoroughly again.
3. Microwave for 1 minute
4. Wait for it to solidify and make a small hole in the middle of the cup, microwave for a further 30 seconds
5. Find a stick (or something similar) that is slightly smaller than your dick, and place it in the middle of the cup. Only place it about 3/4 into the cup (NOT the full way)
6. Place in the refrigerator for 40 mins to an hour
7. Take it out of the glass, it should slide out pretty easily
8. The finished product should be almost like rubber
TIPS: IN step 5, try and use a stick with grooves and patterns