Buy a feeder cup for birds and tie it to the screen with fishing line like I did.
First pic: my chameleon.
Second pic: a stick with a hole drilled thru tied to the screen using fishing line.
Third pic: You can see all my branches are attached that way.
Fourth pic: You can see my chameleon and a tie above his head with fishing line for a branch down below that was too short to tie to the other side.
Fifth pic: See how the feeder cup is attached?
Sixth pic: Fishing line tied in the back
http://imgur.com/a/IHoP4
The reason your worms are falling is because although they have legs they cannot climb as well as crickets do. They won't stay on branches because they are used to being on the ground and will fall off and have no idea where they're going.
Crickets climb on the screen and are easy for the chameleon to find.
Feeder cups are great to put worms in!
Just tie/suction cup the feeder to screen/glass and then put it next to/kinda under his basking branch and he will see the worms and eat out of the cup.
Crickets will even stay in a feeder cup if you place a piece of zucchini, carrot, apple, or orange in it. Only some jump away occasionally.