I read many tickets on the topic of Zooming in WebViews and didnt came to an answer for my case.
Here´s my setup:
I´m using a custom webview with generally
There's a fantastic solution for your issue, based on Javascript (so you'll have to have access to the HTML/JS code in the remote side, if it's the case).
Using the FastClick library, all you need to do is to add the .js file and then call it:
This will get rid of the double tap zoom, and there's still (in my opinion) a huge bonus: all taps get 0.3 seconds faster, due to the fact the system doesn't have to wait anymore for a double tap! Check this example on Android to see the difference: Practical Example
Well, I don't know if this solution will fit in your case, but it was a perfect solution for my Webview projects. Hope it helps!
ps1: you have to add the code above in all pages and frames
ps2: the pinch zoom will keep working normally