They tend to really hate to get directly sprayed in the face/head. I used to mist up in the air above the cage and let it land on Luna - this way she thought SHE was making the decision 
As I posted below, you may want to place him on the plant and then slowly move it into the stream - very slowly - until he is comfy. If he begins to flail his legs move the plant back out. Luna did the same thing and what you need to be careful of is that he doesn't just jump off (thus the towels). He will be jumping blindly b/c his eyes will be closed. If he is settling on the top, and OK with even a small spary of water, that is good. The humidity is there no matter what.
One other thing to take into consideration is that he does not get chilled on the way back to his cage. I would wrap Luna in a non-terry (claws can get stuck in loops) towel and then place her right under her basking light.
How is he doing?
lele
here's Luna in her shower (gravid) and then sitting under her "mist" from the humidifier (btw, if you look closely you can see her MBD in swollen leg joints and bent casque. Houdini does not appear to have it at all)


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Chameleon Help & Resource Info
0.1 Veiled Chameleon - Luna. She's now hanging from her big jungle gym in the sky
1.0 Beardie - Darwin
0.2 felines - Kyndra and Lita
0.1 African Clawed Frog - Skipper
0.1 Mad. Hissers and she is on the loose!
0.1 Chilean Rose Hair Tarantula - Rosa Leigh
0.1 Goliath Bird-Eater Tarantula - Natasha
?.? Pinktoe Tarantula - no name yet